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Inorganica Chimica Acta 359 (2006) 3066–3071

Pyridine and phosphine reactions with [CPh3][B(C6F5)4]

Lourdes Cabrera, Gregory C. Welch, Jason D. Masuda, Pingrong Wei, Douglas W. Stephan *

Department of Chemistry and Biochemistry, University of Windsor, 401 Sunset, Windsor, Ont., Canada N9B 3P4

Received 11 January 2006; accepted 2 February 2006Available online 20 March 2006

Dedicated to Professor Brian James, a Canadian icon of catalysis.

Abstract

Trityl borate salts [4-RPyCPh3][B(C6F5)4] (R = H 1, tBu 2, Et 3, NMe2 4) and [R3PCPh3][B(C6F5)4] (R = Me 5, nBu 6, Ph[1] 7, p-MeC6H4 8) are readily prepared via equimolar reaction of the appropriate pyridine or phosphine and trityl borate [CPh3][B(C6F5)4].The analogous reactions of PiPr3 affords the product [(p-iPr3P–C6H4)Ph2CH][B(C6F5)4] (9) while the corresponding reactions of Cy3Pand tBu3P gave the cyclohexadienyl derivatives [(p-R3PC6H5)CPh2][B(C6F5)4] (R = Cy 10, tBu 11). X-ray structures of 5 and 9 arereported.� 2006 Elsevier B.V. All rights reserved.

Keywords: Trityl borate; Lewis acid–base interaction; Nucleophilic aromatic substitution

1. Introduction

Lewis acidic reagents play important parts in a varietyof stoichiometric and catalytic reactions. In the case ofpolymerization catalysis, Lewis acid reagents such as thetriorganoborane B(C6F5)3 or the carbocation analog[CPh3]+ (trityl) are powerful cocatalysts as these speciesare used to generate catalytically active cationic early metalalkyl complexes as a result of the vacant 2p-orbitals on Band C, respectively. Amines, pyridines and phosphineshave been shown to form simple Lewis acid–base adductswith B(C6F5)3 [2–12]. More recently, we have shown thatreactions of (THF)B(C6F5)3 with sterically demandingphosphines leads not to simple donor exchange but ratherto controlled THF-ring opening reactions [13]. In the caseof the trityl cation, donor–acceptor adducts have been pre-viously reported [14–19], however the role of steric bulk hasnot been extensively probed. In this paper, the reactions ofpyridines and phosphines with the Lewis acid trityl borate[CPh3][B(C6F5)4] are probed. The role of significant steric

0020-1693/$ - see front matter � 2006 Elsevier B.V. All rights reserved.

doi:10.1016/j.ica.2006.02.006

* Corresponding author. Fax: +519 973 7098.E-mail address: stephan@uwindsor.ca (D.W. Stephan).

demands is shown to alter the reaction course, affordingnucleophilic aromatic attack and substitution.

2. Experimental

General data: All preparations were done under anatmosphere of dry, O2-free N2 employing both Schlenk linetechniques and a Vacuum Atmospheres inert atmosphereglove box. Solvents were purified employing a Grubbs’type solvent purification system manufactured by Innova-tive Technology. Deuterated solvents were purified usingthe appropriate techniques. All organic reagents were puri-fied by conventional methods. 1H, and 13C{1H} NMRspectra were recorded on Bruker Avance-300 and 500 spec-trometers. All NMR spectra were recorded in C6D6 at25 �C. Trace amounts of protonated solvents were usedas references and chemical shifts are reported relative toSiMe4. Combustion analyses were done in house employ-ing a Perkin–Elmer CHN Analyzer. [CPh3][B(C6F5)4] wasgenerously donated by Nova Chemicals Co. The reagentsPy, 4-EtPy, 4-tBuPy, 4-DMAP, PMe3 (1.0 M in toluene),PCy3 and PtBu3 were purchased from Aldrich ChemicalCo. PMe3, PCy3 and PtBu3 were used as received. Py,

L. Cabrera et al. / Inorganica Chimica Acta 359 (2006) 3066–3071 3067

4-EtPy and 4-tBuPy were dried over CaH2 and fractionallydistilled, then stored in contact with 4 A molecular sieves.4-DMAP was recrystallized from toluene prior to use.PiPr3, PnBu3, P(p-CH3C6H4)3 and P(o-CH3C6H4)3 wereobtained from Strem Chemicals and used as received.PPh3 was obtained from Strem Chemicals and recrystal-lized from pentanes prior to use.

2.1. Synthesis of [4-RPyCPh3][B(C6 F5)4] R = H 1, tBu 2,

Et 3, NMe2 4

These compounds were prepared in a similar mannerusing the appropriate substituted pyridine 4-RPy (R = H,Et, tBu, NMe2), and thus only a representative preparationis detailed. To a solution of [CPh3][B(C6F5)4] (64 mg,0.07 mmol) in CH2Cl2 (4 mL), a solution of 4-RPy(0.07 mmol) in CH2Cl2 (2 mL) was added at RT. The mix-ture was stirred for 30 min, after which time the solventwas reduced in vacuo to ca. 1 mL. Addition of pentane tothe CH2Cl2 solution resulted in the formation of a precipi-tate. The solvent was decanted and the precipitate was driedin vacuo. 1 (136 mg, 97%). 1H NMR (CD2Cl2): 8.76 (d, 2H,3JH–H = 6 Hz, C5H5N, (a-H)), 8.54 (t, 1H, 3JH–H = 7 Hz,C5H5N, (c-H)), 7.99 (t, 2H, 3JH–H = 7 Hz, C5H5N, (b-H)),7.51–7.45 (m, 9H, CPh3, o,p-H), 7.15 (m, 6H, CPh3, m-H).13C{1H} NMR (CD2Cl2): 148.6 (d(m), 1JC–F = 227 Hz,C6F5 (o-C)), 145.2 (s, C5H5N, (a-C)), 138.6 (s, CPh3, (ipso-C)), 138.8 (d(m), 1JC–F = 250 Hz, C6F5 (p-C)), 136.9 (d(m),1JC–F = 241 Hz, C6F5 (m-C)), 130.7 (s, C5H5N, (c-C)),130.6 (s, CPh3, (o,m-C)), 130.0 (s, CPh3, (p-C)), 128.3 (s,C5H5N, (b-C)), 124.5 (s, br, C6F5 (ipso-C)), 91.0 (s, CPh3).11B{1H} NMR (CD2Cl2): �17.0 (s). 19F NMR (CD2Cl2):�133.39 (s, 8F, C6F5 (o-F)), �163.82 (t, 4F, 3JF–F = 20 Hz,C6F5 (p-F)),�167.72 (t, 8F, 3JF–F = 17 Hz, C6F5 (m-F)). Ele-mental Anal. Calc. for C48H20BF20N: C, 57.57; H, 2.01; N,1.04. Found: C, 57.71; H, 2.24; N, 1.11%. 2: (61 mg, 82%).1H NMR (CD2Cl2): 8.58 (d, 2H, 3JH–H = 7 Hz,4-tBuC5H4N, (a-H)), 7.90 (d, 2H, 3JH–H = 7 Hz,4-tBuC5H4N, (b-H)), 7.50–7.43 (m, 9H, CPh3, (o,p-H)),7.14 (m, 6H, CPh3, (m-H)), 1.42 (s, 9H, 4-tBuC5H4N).13C{1H} NMR (CD2Cl2): 174.9 (s, 4-tBuC5H4N, (c-C)),148.7 (d(m), 1JC–F = 241 Hz, C6F5 (o-C)), 144.3 (s,4-tBuC5H4N, (a-C)), 138.8 (d(m), 1JC–F = 247 Hz, C6F5 (p-C)), 138.8 (s, CPh3, (ipso-C)), 136.8 (d(m), 1JC–F = 244 Hz,C6F5 (m-C)), 128.7 (s, br, C6F5 (ipso-C)), 130.5 (s, CPh3,(o,m-C)), 129.8 (s, CPh3, (p-C)), 125.2 (s, 4-tBuC5H4N, (b-C)), 89.9 (s, CPh3), 37.5 (s, 4-tBuC5H4N), 30.1 (s,4-tBuC5H4N). 11B{1H} NMR (CD2Cl2): �17.0 (s). 19FNMR (CD2Cl2): �133.33 (s, 8F, C6F5 (o-F)), �163.85 (t,4F, 3JF–F = 20 Hz, C6F5 (p-F)), �167.73 (t, 8F, 3JF–F =17 Hz, C6F5 (m-F)). Elemental Anal. Calc. forC52H28BF20N: C, 59.06; H, 2.67; N, 1.32. Found: C, 59.12;H, 2.78; N, 1.48%. 3: (70 mg, 97%). 1H NMR (CD2Cl2) d:8.56 (d, 2H, 3JH–H = 7 Hz, 4-EtC5H5N, (a-H)), 7.75 (d,2H, 3JH–H = 7 Hz, 4-EtC5H5N, (b-H)), 7.51–7.44 (m, 9H,CPh3, o,p-H), 7.14 (m, 6H, CPh3, m-H), 2.99 (q, 2H, 3JH–H =8 Hz, 4-EtC5H5N), 1.37 (t, 3H, 3JH–H = 8 Hz, 4-EtC5H5N).

13C{1H} NMR (CD2Cl2): 162.8 (s, 4-Et-C5H4N, (c-C)),148.8 (d(m), 1JC–F = 244 Hz, C6F5 (o-C)), 144.2 (s, 4-EtC5H4N, (a-C)), 138.9 (s, CPh3, (ipso-C)), 138.8 (d(m),1JC–F = 244 Hz, C6F5 (p-C)), 136.8 (d(m), 1JC–F = 249 Hz,C6F5 (m-C)), 130.5 (s, CPh3, (o,m-C)), 129.9 (s, CPh3,(p-C)), 127.3 (s, 4-EtC5H4N, (b-C)), 124.7 (s, br, C6F5

(ipso-C)), 89.7 (s, CPh3), 29.6 (s, 4-EtC5H4N), 13.2 (s, 4-EtC5H4N). 11B{1H} NMR (CD2Cl2): �17.0 (s). 19F NMR(CD2Cl2): �133.35 (s, 8F, C6F5 (o-F)), �163.82 (t, 4F, 3JF–F =20 Hz, C6F5 (p-F)), �167.70 (t, 8F, 3JF–F = 17 Hz, C6F5

(m-F)). Elemental Anal. Calc. for C50H24BF20N: C, 58.33;H, 2.35; N, 1.36. Found: C, 57.91; H, 2.66; N, 1.38%. 4:(68 mg, 93%).1H NMR (CD2Cl2): 7.95 (d, 2H, 3JH–H =8 Hz, 4-Me2NC5H4N, (a-H)), 7.43 (m, 6H, CPh3, (m-H)),7.18 (m, 9H, CPh3, (o,p-H)), 6.67 (d, 2H, 3JH–H = 8 Hz, 4-Me2NC5H4N, (b-H)), 3.21 (s, 6H, 4-Me2NC5H4N).13C{1H} NMR (CD2Cl2): 156.8 (s, 4-Me2NC5H4N, (c-C)),148.8 (d(m), 1JC–F = 242 Hz, C6F5 (o-C)), 144.2 (s,4Me2NC5H4N, (a-C)), 138.9 (s, CPh3, (ipso-C)), 138.9(d(m), 1JC–F = 242 Hz, C6F5 (p-C)), 136.9 (d(m), 1JC–F =248 Hz, C6F5 (m-C)), 130.5 (s, CPh3, (o,m-C)), 129.6 (s,CPh3, (p-C)), 129.3 (s, 4-Me2NC5H4N, (b-C)), 124.7 (s, br,C6F5 (ipso-C)), 89.7 (s, CPh3), 40.7 (s, 4-Me2N-C5H4N).11B{1H} NMR (CD2Cl2): �16.9 (s). 19F NMR (CD2Cl2):�133.38 (s, 8F, C6F5 (o-F)), �163.95 (t, 4F, 3JF–F = 20 Hz,C6F5 (p-F)),�167.81 (t, 8F, 3JF–F = 17 Hz, C6F5 (m-F)). Ele-mental Anal. Calc. for C50H25BF20N2: C, 57.49; H, 2.41; N,2.68. Found: C, 57.32; H, 2.50; N, 2.75%.

2.2. Synthesis of [R3PCPh3][B(C6F5)4] R = Me 5, nBu 6,Ph[1] 7, p-MeC6H4 8, and

[(p-iPr3PC6H4)Ph2CH][B(C6F5)4] 9,

[(p-R3PC6H5)CPh2][B(C6F5)4] R = Cy 10, tBu3 11

These compounds were prepared in a similar mannerusing the appropriate tertiary phosphine PR3 (R = Me,nBu, Ph, p-CH3C6H4, iPr, Cy, tBu), and thus only a repre-sentative preparation is detailed. To a solution of[CPh3][B(C6F5)4] (64 mg, 0.07 mmol) in CH2Cl2 (4 mL), asolution of PR3 (0.07 mmol) in CH2Cl2 (2 mL) was addedat RT. The mixture was stirred for 30 min, after which timethe solvent was reduced in vacuo to ca. 2 mL. Addition ofpentane to the CH2Cl2 solution resulted in the formation ofa precipitate. The solvent was decanted and the precipitatewas dried in vacuo. 5: orange solid (57 mg, 83%). 1H NMR(CD2Cl2): 7.50 (m, 9H, CPh3, (o,p-H)), 7.07 (m, 6H, CPh3,(m-H)), 1.95 (d, 9H, 3JH–H = 12 Hz, PMe3). 13C{1H} NMR(CD2Cl2): 148.8 (d(m), 1JC–F = 241 Hz, C6F5 (o-C)), 138.8(d(m), 1JC–F = 243 Hz, C6F5 (p-C)), 137.5 (s, CPh3, (ipso-C)), 136.9 (d(m), 1JC–F = 244 Hz, C6F5 (m-C)), 130.3 (s,CPh3, (o,m,p-C)), 124.8 (s, br, C6F5 (ipso-C)), signal forCPh3 was not observed, 13.4 (d, 1JC–F = 52 Hz, PMe).11B{1H} NMR (CD2Cl2): �16.9 (s). 19F NMR (CD2Cl2):�133.18 (s, 8F, C6F5 (o-F)), �163.80 (t, 4F, 3JF–F =20 Hz, C6F5 (p-F)), �167.63 (t, 8F, 3JF–F = 17 Hz, C6F5

(m-F)). 31P{1H} NMR (CD2Cl2): 38.7 (s). Elemental Anal.Calc. for C46H24BF20P: C, 55.34; H, 2.42. Found: C, 55.37;

3068 L. Cabrera et al. / Inorganica Chimica Acta 359 (2006) 3066–3071

H, 1.84%. 6: white solid (68 mg, 87%). 1H NMR (CD2Cl2):7.51–7.44 (m, 9H, CPh3), 7.07 (m, 6H, CPh3, 2.25 (m, 6H,PCH2CH2), 1.34 (m, 12H, PCH2CH2CH2CH3), 0.82 (t, 9H,3JH–H = 7 Hz, CH2CH3). 13C{1H} NMR (CD2Cl2): 148.8(d(m), 1JC–F = 244 Hz, C6F5 (o-C)), 138.8 (d(m), 1JC–F =246 Hz, C6F5 (p-C)), 138.0 (s, CPh3, (ipso-C)), 136.9(d(m), 1JC–F = 250 Hz, C6F5 (m-C)), 130.7 (d, 3JP–C =5 Hz, CPh3, (o,m-C)), 130.4 (s, CPh3, (p-C)), 130.3 (s,CPh3, (p-C)), 124.8 (s, br, C6F5 (ipso-C)), 65.0 (d, 1JP–C =38 Hz, CPh3), 26.2 (d, 1JP–C = 6 Hz, PCH2), 24.6 (d,2JP–C = 15 Hz, PCH2CH2), 23.4 (d, 3JP–C = 41 Hz,CH2CH2CH3), 13.3 (s, CH2CH3). 11B{1H} NMR(CD2Cl2): �16.8 (s). 19F NMR (CD2Cl2): �133.31 (s, 8F,C6F5 (o-F)), �164.02 (t, 4F, 3JF–F = 21 Hz, C6F5 (p-F)),�167.86 (s, 8F, C6F5 (m-F)). 31P{1H} NMR (CD2Cl2):42.8 (s). Elemental Anal. Calc. for C55H42BF20P: C,58.74; H, 3.76. Found: C, 58.28; H, 3.69%. 7: white solid(73 mg, 89%). 1H NMR (CD2Cl2): 7.79 (d, 3H, 3JH–H =8 Hz, PPh3, (p-H)), 7.54 (d, 3H, 3JH–H = 8 Hz, CPh3, (p-H)), 7.33 (t, 6H, 3JH–H = 8 Hz, CPh3, (m-H)), 7.46 (dd,6H, 3JH–H = 8 Hz, 4JP–H = 3 Hz, PPh3, (m-H)), 7.00 (d,6H, 3JH–H = 8 Hz, CPh3, (o-H)), 6.83 (m, 6H, PPh3, (o-H)). 13C{1H} NMR (CD2Cl2): 148.9 (d(m), 1JC–F =240 Hz, C6F5 (o-C)), 138.8 (d(m), 1JC–F = 249 Hz,C6F5(p-C)), 136.9 (d(m), 1JC–F = 242 Hz, C6F5(m-C)),135.9 (s, CPh3, ((ipso-C))), 135.7 (d, 2JP–C = 8 Hz, PPh3,(o-C)), 132.6 (d, 4JP–C = 5 Hz, PPh3, (p-C)), 131.0 (s,PPh3 (m-C)), 130.9 (s, CPh3, (o,m-C)), 129.8 (s, CPh3, (p-C)), 120.9 (d, 1JP–C = 75 Hz, PPh3, (ipso-C)), 124.0 (s, br,C6F5 (ipso-C)), signal for CPh3 was not observed.11B{1H} NMR (CD2Cl2): �16.9 (s). 19F NMR (CD2Cl2):�133.43 (s, 8F, C6F5 (o-F)), �164.10 (t, 4F, 3JF–F =21 Hz, C6F5 (p-F)), �167.93 (t, 8F, 3JF–F = 17 Hz, C6F5

(m-F)). 31P{1H} NMR (CD2Cl2): 24.6 (s). Elemental Anal.Calc. for C61H30BF20P: C, 61.85; H, 2.55. Found: C, 61.30;H, 2.90%. 8: white solid (77 mg, 91%). 1H NMR (CD2Cl2):7.52 (t, 3H, 3JH–H = 8 Hz, CPh3, (p-H)), 7.33 (t, 6H, 3JH–H =8 Hz, CPh3, (m-H)), 7.25 (dd, 6H, 3JH–H = 8 Hz, 4JP–H = 3Hz, P(p-MeC6H4)3, (m-H)), 7.03 (d, 6H, 3JH–H = 8 Hz,CPh3, (o-H)), 6.71 (m, 6H, P(p-MeC6H4)3, (o-H)), 2.44 (s,9H, P(p-MeC6H4)3). 13C{1H} NMR (CD2Cl2): 148.9(d(m), 1JC–F = 241 Hz, C6F5 (o-C)), 147.6 (s, CPh3, (ipso-C)), 138.9 (d(m), 1JC–F = 245 Hz, C6F5 (p-C)), 136.9(d(m), 1JC–F = 250 Hz, C6F5 (m-C)), 135.7 (d, 2JP–C =9 Hz, P(p-MeC6H4)3, (o-C)), 132.7 (d, 4JP–C = 5 Hz, P(p-MeC6H4)3, (p-C)), 131.7 (d, 3JP–C = 12 Hz, P(p-MeC6H4)3

(m-C)), 130.6 (s, CPh3, (o,m-C)), 129.7 (s, CPh3, (p-C)),124.7 (s, br, C6F5 (ipso-C)), 117.8 (d, 1JP–C = 78 Hz, P(p-MeC6H4)3 (ipso-C)), 68.6 (d, 1JP–C = 41 Hz, CPh3), 21.9(s, P(p-MeC6H4)3). 11B{1H} NMR (CD2Cl2): �16.8 (s).19F NMR (CD2Cl2): �133.35 (s, 8F, C6F5 (o-F)),�164.02 (t, 4F, 3JF–F = 20 Hz, C6F5 (p-F)), �167.79 (t,8F, 3JF–F = 15 Hz, C6F5 (m-F)). 31P{1H} NMR (CD2Cl2):24.6 (s). Elemental Anal. Calc. for C64H36BF20P: C, 62.66;H, 2.96; N, 0.00. Found: C, 62.50; H, 2.64; N, 0.07%. 9:pink solid (63 mg, 84%). 1H NMR (CD2Cl2): 7.60–7.11(m, 14H, (p-iPr3PC6H4)Ph2CH), 5.69 (s, 1H, (p-iPr3PC6H4)

Ph2CH), 3.00 (m, 3H, 3JH–H = 7 Hz, iPr), 1.39 (dd, 18H,3JH–H = 7 Hz, 3JP–H = 16 Hz, iPr). 13C{1H} NMR(CD2Cl2): 152.6 (s, (p-iPr3PC6H4)Ph2CH, (p-C), 148.3 (d(m),1JC–F = 239 Hz, C6F5 (o-C)), 142.2 (s, (p-iPr3PC6H4)Ph2CH, (ipso-C)), 138.4 (d(m), 1JC–F = 246 Hz, C6F5 (p-C)), 136.5 (d(m), 1JC–F = 246, C6F5 (m-C)), 132.6 (s,(p-iPr3PC6H4)Ph2CH, (o-C)), 131.8 (d, 2JP–C = 11 Hz,(p-iPr3PC6H4)Ph2CH, (m-C)), 129.4 (s, (p-iPr3PC6H4)Ph2CH, (m-C)), 128.9 (s, (p-iPr3P–C6H4)Ph2CH, (o-C)),127.2 (s, (p-iPr3PC6H4)Ph2CH, (p-C)), 124.8 (s, br, C6F5

(ipso-C)), 110.1 (d, 1JP–C = 75 Hz, (p-iPr3PC6H4)Ph2CH,(p-C)), 56.9 (s, (p-iPr3P–C6H4)Ph2CH), 21.1 (d, 1JP–C =43 Hz, PiPr), 16.4 (s, iPr). 11B{1H} NMR (CD2Cl2):�17.0 (s). 19F NMR (CD2Cl2): �133.33 (s, 8F, C6F5 (o-F)), �163.91 (t, 4F, 3JF–F = 20 Hz, C6F5 (p-F)), �167.80(s, br, 8F, C6F5 (m-F)). 31P{1H} NMR (CD2Cl2): 40.4 (s).Elemental Anal. Calc. for C52H36BF20P: C, 57.69; H,3.35. Found: C, 57.74; H, 3.71%. 10: yellow solid (75 mg,89%). 1H NMR (CD2Cl2): 7.37 (m, 6H, (4-Cy3PC6H5)CPh2, (p,o-H)), 7.15 (dd, 4H, 3JH–H = 8 Hz, 4JH–H = 2 Hz(4-Cy3PC6H5)CPh2, (m-H)), 6.86 (d(m), 2H, 3JH–H =10 Hz, (4-Cy3PC6H5)CPh2, (2-H)), 5.69 (m, 2H, 3JH–H =10 Hz, (4-Cy3PC6H5)CPh2, (3-H)), 4.46 (d(m), 2JP–H = 28Hz, (4-Cy3PC6H5)CPh2, (4-H)), 1.33–2.45 (m, br, 33H,PCy3). 13C{1H} NMR (CD2Cl2): 148.7 (d(m), 1JC–F =237 Hz, C6F5 (o-C)), 140.8 (d, 5JP–C = 4 Hz, (4-PCy3-C6H5)CPh2), 138.1 (d(m), 1JC–F = 244 Hz, C6F5 (p-C)),136.9 (d(m), 1JC–F = 257, C6F5 (m-C)), 134.5 (d, 3JP–C =11 Hz, (4-Cy3PC6H5)CPh2 (2-C)), 130.6 (s, (4-Cy3PC6H5)CPh2, (o-C)), 129.3 (s, (4-Cy3PC6H5) CPh2, (ipso-C)), 129.0(s, (4-Cy3PC6H5)CPh2, (p-C)), 128.9 (s, (4-Cy3PC6H5)CPh2, (m-C)), 125.8 (d, 4JP–C = 11 Hz, (4-Cy3PC6H5)CPh2

(1-C)), 124.2 (s, br, C6F5 (ipso-C)), 118.3 (d, 2JP–C = 9 Hz,(4-Cy3PC6H5)CPh2 (3-C)), 33.7 (d, 1JP–C = 42 Hz, PCy3 (1-C)), 32.0 (d, 1JP–C = 35 Hz, 4-Cy3PC6H5)CPh2, (4-C)), 28.0(d, 3JP–C = 4 Hz, PCy3 (3-C)), 27.5 (d, 2JP–C = 11 Hz, PCy3

(2-C)), 25.4 (s, PCy3 (4-C)). 11B{1H} NMR (CD2Cl2):�16.8 (s). 19F NMR (CD2Cl2): �133.31 (s, 8F, C6F5 (o-F)), �163.94 (t, 4F, 3JF–F = 20 Hz, C6F5 (p-F)), �167.74(t, 8F, 3JF–F = 17 Hz, C6F5 (m-F)). 31P{1H} NMR(CD2Cl2): 28.1 (s, PCy3). Elemental Anal. Calc. forC61H48BF20P: C, 60.91; H, 4.02. Found: C, 60.72; H,3.83%. 11: yellow solid (67 mg, 86%). 1H NMR (CD2Cl2):7.36 (m, 6H, (4-tBu3PC6H5)CPh2, (m,p-H)), 7.14 (m, 4H,(4-tBu3PC6H5)CPh2, (o-H)), 6.87 (d(m), 2H, 3JH–H = 10 Hz,(4-tBu3PC6H5)CPh2, (2-H)), 6.12 (d(m), 2H, 3JH–H =10 Hz, (4-tBu3PC6H5)CPh2, (3-H)), 4.67 (d(m), 1H,2JP–H = 27 Hz, (4-tBu3PC6H5)CPh2, (4-H)), 1.71 (d, 27H,3JP–H = 14 Hz, P(CMe3). 13C{1H} NMR (CD2Cl2): 148.8(d(m), 1JC–F = 240 Hz, C6F5 (o-C)), 140.7(d, 5JP–C =4 Hz, (4-tBu3PC6H5)CPh2), 138.8 (d(m), 1JC–F = 245 Hz,C6F5 (p-C)), 136.9 (d(m), 1JC–F = 246 Hz, C6F5 (m-C)),134.4 (d, 3JP–C = 10 Hz, (4-tBu3PC6H5)CPh2, (2-C)),130.8 (s, (4-tBu3PC6H5)CPh2, (o-C)), 129.0 (s,(4-tBu3PC6H5)CPh2, (p-C)), 128.9 (s, (4-tBu3PC6H5)-CPh2, (m-C)) 128.5 (s, (4-tBu3PC6H5)CPh2, (ipso-C)),125.3 (d, 4JP–C = 10 Hz, (4-tBu3PC6H5)CPh2, (1-C)),

Table 1Crystallographic parameters

1 9

Molecular formula C46H24BPF20 C52H36BPF20 Æ CH2Cl2Formula weight 998.43 1166.51a (A) 10.2445(15) 10.901(5)b (A) 13.955(2) 13.168(6)c (A) 15.222(2) 19.539(9)a (�) 101.361(2) 96.262(9)b (�) 95.597(2) 100.806(9)c (�) 103.344(2) 109.261(8)Crystal system triclinic triclinicSpace group P�1 P�1Volume (A3) 2052.5(5) 2556(2)Dcalc (g cm�3) 1.616 1.515Z 2 2Absorption coefficient, l(mm�1) 0.194 0.269h Range (�) 1.82–25.00 2.07–23.27Reflections collected 19923 10903Data F 2

o > 3rðF 2oÞ 7211 7281

Parameters 616 694R(%) 0.0613 0.0674Rw(%) 0.1241 0.1955Goodness-of-fit 0.975 1.016

The data were collected at 20 �C with Mo Ka radiation (k = 0.71073 A).

R ¼PjjF oj � jF cjj=

PjF oj, Rw ¼

PðjF oj � jF cjÞ2j=

PjF oj2

h i0:5.

L. Cabrera et al. / Inorganica Chimica Acta 359 (2006) 3066–3071 3069

124.2 (s, br, C6F5 (ipso-C)), 121.0 (d, 2JP–C = 10 Hz,(4-tBu3PC6H5)CPh2, (3-C)), 42.3 (d, 1JP–C = 21 Hz, tBu,38.9 (d, 1JP–C = 31 Hz, 4-tBu3PC6H5)CPh2, (4-C)), 31.0(s, tBu). 11B{1H} NMR (CD2Cl2): �16.8 (s). 19F NMR(CD2Cl2): �133.28 (s, 8F, C6F5 (o-F)), �163.85 (t, 4F,3JF–F = 20 Hz, C6F5 (p-F)), �167.73 (d, 8F, 3JF–F =17 Hz, C6F5 (m-F)). 31P{1H} NMR (121.5 MHz, CD2Cl2):50.2 (s, tBu3PC6H5). Elemental Anal. Calc. forC55H42BF20P: C, 58.74; H, 3.76. Found: C, 58.02; H,3.61%.

2.3. X-ray data collection and reduction

Crystals were manipulated and mounted in capillaries ina glove box, thus maintaining a dry, O2-free environmentfor each crystal. Diffraction experiments were performedon a Siemens SMART System CCD diffractometer. Thedata were collected in a hemisphere of data in 1448 frameswith 10 s exposure times. The observed extinctions wereconsistent with the space groups in each case. The data setswere collected (4.5� < 2h < 45–50.0�). The intensities ofreflections within these frames showed no statistically sig-nificant change over the duration of the data collections.The data were processed using the SAINT and XPREP process-ing packages. An empirical absorption correction based onredundant data was applied to each data set. Subsequentsolution and refinement was performed using the SHELXTL

solution package.

2.4. Structure solution and refinement

Non-hydrogen atomic scattering factors were takenfrom the literature tabulations.[20] The heavy atom posi-tions were determined using direct methods employingthe SHELXTL direct methods routine. The remaining non-hydrogen atoms were located from successive differenceFourier map calculations. The refinements were carriedout by using full-matrix least squares techniques on F,minimizing the function x (Fo � Fc)

2 where the weight xis defined as 4F 2

o=2rðF 2oÞ and Fo and Fc are the observed

and calculated structure factor amplitudes. In the finalcycles of each refinement, all non-hydrogen atoms wereassigned anisotropic temperature factors in the absenceof disorder or insufficient data. In the latter cases atomswere treated isotropically. In the case of compound 1

the methyl group of toluene was modeled by a 50:50two-site disorder. C–H atom positions were calculatedand allowed to ride on the carbon to which they arebonded assuming a C-H bond length of 0.95 A. H-atomtemperature factors were fixed at 1.10 times the isotropictemperature factor of the C-atom to which they arebonded. The H-atom contributions were calculated, butnot refined. The locations of the largest peaks in the finaldifference Fourier map calculation as well as the magni-tude of the residual electron densities in each case wereof no chemical significance. Additional details are pro-vided in the supplementary data and Table 1.

3. Results and discussion

Trityl pyridinium borate salts [4-RPyCPh3][B(C6F5)4]R = H 1, tBu 2, Et 3, NMe2 4 are readily prepared via equi-molar reaction of the appropriate pyridine and trityl borate[CPh3][B(C6F5)4]. Solutions of the reaction mixtures wereprepared in CH2Cl2, mixed at room temperature and leftto stir for 30 min. The resulting trityl pyridinium borate salts1–4 were subsequently isolated and characterized by 1H,13C{1H}, 11B{1H} and 19F{1H} NMR methods. The 1HNMR chemical shifts of the pyridine b-ring protons for thepyridinium compounds are downfield of the free pyridinedue to coordination to the trityl cation. In the case of 4 thepyridine ring a-protons are shifted upfield with respect tothe corresponding protons of the free pyridine 4-DMAP.This is the only pyridinium cation that shows this phenome-non and is attributed to the presence of the electron donatingNMe2-substituent. 11B{1H} and 19F NMR spectra for eachpyridinium borate salt 1–4 were similar indicating theabsence of interactions between the borate anion and thepyridinium cations.

Similar reactions between pyridines and trityl salts havepreviously been reported [15,16,18]. Briegleb showed thereaction between pyridines and [CPh3]+ are reversible anddependent on the concentration of the pyridine and solvent[15] while Damico and Broaddus reported trityl salts with avariety of tertiary amines, secondary amines and pyridines[16].

Analogous reactions of [CPh3][B(C6F5)4] with tertiaryphosphines were performed in CH2Cl2. In this manner,the phosphonium salts [R3PCPh3][B(C6F5)4] R = Me 5,nBu 6, Ph[1] 7, p-MeC6H4 8 were synthesized and character-ized by NMR spectroscopy. 1H and 13C{1H} NMR spectra

Fig. 3. ORTEP diagram of [(p-iPr3PC6H4)Ph2CH][B(C6F5)4] (9), hydro-gen atoms are omitted for clarity; 50% thermal ellipsoids. P(1)–C(17)1.804(4) A.

3070 L. Cabrera et al. / Inorganica Chimica Acta 359 (2006) 3066–3071

were as expected while the 31P{1H} NMR chemical shiftswere significantly shifted downfield from the chemical shiftof the corresponding free phosphines. As with above pyri-dine complexes, the 11B{1H} and 19F NMR spectra forthese phosphonium borate salts 5–8 showed resonances typ-ical of the free anion. Compound 5 was also characterizedcrystallographically (Fig. 1). The P–C(trityl) distance wasfound to be 1.887(4) A, typical of P–C bond length. Theremaining metric parameters are unexceptional.

The analogous reactions of PiPr3 with [CPh3][B(C6F5)4]results in the formation of the product 9 that exhibits 1Hand 13C{1H} NMR data that are not consistent with the for-mation of a phosphonium salt analogous to 5–8. The 1HNMR spectrum of 9 (Fig. 2) showed a signal at 5.69 ppmwith an integration value of one proton. In addition, the13C{1H} NMR spectrum showed no signal at ca. 67 ppm,where signals for quaternary carbocations of 5–8 areobserved. Instead compound 9 exhibits a 13C{1H} NMR sig-nal at ca. 56.9 ppm. These data suggest the formulation ofthe product [(p-iPr3P–C6H4)Ph2CH][B(C6F5)4] (9). Thisstructural formulation was confirmed by X-ray crystallo-graphic analysis (Fig. 3). The P–C(arene) bond distancewas found to be 1.804(4) A, again typical of P–C single bond.The other metric parameters were as expected (Table 1).

In contrast, the reactions involving PR3 (R = Cy, tBu)and [CPh3][B(C6F5)4] gave new products 10 and 11. These

Fig. 2. 1H NMR spectrum of the ca

Fig. 1. ORTEP diagram of [Me3PCPh3][B(C6F5)4] (1), hydrogen atomsare omitted for clarity; 50% thermal ellipsoids. P(1)–C(25) 1.887(4) A.

species were not either type of phosphonium salts describedabove ([R3PCPh3][B(C6F5)4] or [(p-R3PC6H4)Ph2CH]-[B(C6F5)4]). In these cases, the 1H NMR spectra showedthree sets of doublets at ca. 6.80, 6.00 and 4.50 ppm. integrat-ing to 2:2:1 protons, respectively (Fig. 4). The 13C{1H} NMRspectra show resonance signals at ca. 134.4, 125.6 and119.7 ppm, that correlate to the signals in the doublets in1H NMR spectra. In addition, 13C{1H} NMR signals corre-sponding to the central trityl carbon atom was observed atca.140.8 ppm. These data support the formulation of 10

and 11 as [p-R3P(C6H5)CPh2][B(C6F5)4] R = Cy, tBu3, spe-cies containing cyclohexadienyl moieties (Scheme 1). Forboth 10 and 11, DEPT spectra confirmed the presence ofthe cyclohexadienyl moieties.

Previous research involving phosphines and trityl boratedescribed the formulation of phosphonium salts[1,17,19,21]. A report by Bidan and Genies [14] showedthe steric demands of the R-groups present in the phos-phine determined the course of the reaction affording either[p-benzhydryl-phenyl]-phosphonium or tritylphosphoniumsalts. They proposed a reaction mechanism involving theformation of [4-benzhydrylidene-cyclohexadienyl]phospho-nium salts that undergoes subsequent rearrangement to[p-benzhydryl-phenyl]-phosphonium salt (Scheme 1). This

tion [(p-iPr3PC6H4)Ph2CH]+ (9).

Fig. 4. 1H NMR spectrum of [(p-tBu3PC6H5)CPh2][B(C6F5)4] (11).

[CPh3][B(C6F5)4]

L

[RC5H4NCPh3][B(C6F5)4]

R = H 1, tBu 2, Et 3, NMe2 4

R = Me 5 nBu 6, Ph 7 MeC6H4 8

[B(C6F5)4]

CHPh2R3P

R = iPr 9

CPh2R3P

[B(C6F5)4]

R = Cy 10, tBu 11

H

[R3PCPh3][B(C6F5)4]

Scheme 1.

L. Cabrera et al. / Inorganica Chimica Acta 359 (2006) 3066–3071 3071

mechanism accounts for the isolation of 9–11. It is alsonoteworthy that monitoring the reaction of PiPr3 and[CPh3][B(C6F5)4] immediately after mixing revealed thepresence of two species, an intermediate formulated as[p-iPr3P(C6H5)CPh2][B(C6F5)4] and 9. The former speciesis rapidly transformed to 9.

These findings reveal that sterically unencumbereddonors such as pyridines and small phosphines react withthe trityl cation to give simple Lewis acid–base adducts.In contrast, sterically demanding phosphines are too largeto interact with the central carbon of the carbocation andinstead effect nucleophilic aromatic substitution at a posi-tion para to the central trityl carbon involving the conver-sion of a cylcohexadienyl derivative to the correspondingbenzylhydryl-phenyl species.

Acknowledgement

Financial support from NSERC of Canada is gratefullyacknowledged. J.D.M. is grateful for the award of an On-tario Graduate Scholarship and a Bayer Inc. Award fromthe Macromolecular Science and Engineering Division ofthe Canadian Institute for Chemistry.

Appendix A. Supplementary data

Available Crystallographic information (CIF) has alsobeen deposited. Supplementary data associated with thisarticle can be found, in the online version, at doi:10.1016/j.ica.2006.02.006.

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