Polyhedron Vol. 8, No. 8, pp. 106’S107X1989 Printed in Great Britain

0277-5387/89 $3.00 + .oO 0 1989 Pergamon Press pit

SUBSTITUTION REACTIONS IN CYCLOMETALLATED COMPLEXES. CRYSTAL AND MOLECULAR STRUCTURE OF

[(C,H,N)(Me,P)h(CH,CMe,-t&HJ]

ERNEST0 CARMONA,? MARGARITA PANEQUE and MANUEL L. POVEDA

Departamento de Quimica Inorganica, Instituto de Ciencia de Materiales, Universidad de Sevilla-CSIC, 41071 Sevilla, Spain

and

ENRIQUE GUTIERREZ-PUEBLA and ANGELES MONGE

Instituto de Ciencia de Materiales, Sede D, CSIC. Serrano 113, 28006 Madrid, Spain and Facultad de Ciencias Quimicas, Universidad Complutense de Madrid, 28040 Madrid, Spain

(Received 19 September 1988; accepted 10 November 1988)

Abstract-The interaction of the cyclometallated complex [(Me3P)2Ni(CHzCMe2-o-C6H4)] with the mono or bidentate N- and P-donor ligands CSH5N (py), Me2NCH2CH2NMe2 (tmen), PMezPh and Me,PCH2CH,PMe2 (dmpe), has been studied. Of these, only py and dmpe afford the substitution products, [(C,HSN)(Me,P)Ni(CH,CMe,-o-&H,)] (2) and [(dmpe)Ni(CH,CMe~-o-CeH4)] (4), in clean, high yield reactions. Isolation of the tmen derivative has proved unattainable, while the PMe*Ph complex [(PhMe,P)2NwH$Me2- xeH4)] (3), is best obtained by alkylation of wiC12(PMe,Ph),] with Mg(CH,CMe,Ph)Cl, in the presence of II. The new compounds 2-4 have been characterized by analytical and spectroscopic studies, and in the case of 2, an X-ray structural determination has also been undertaken. Compound 2 is monoclinic, space group P2,/c, with unit cell parameters a = 9.154(2), b = 10.810(2), c = 19.240(10) A, /I = 102.3(l)“ and Dcalc = 1.23 g cmp3 for Z = 4. The nickel centre is in a slightly distorted square-planar environment, with Ni-C(ary1) and Ni-C(alky1) distances of 1.917(S) and 1.935(5) A, respectively.

Transition metal-metallacycles have been subjected to numerous studies in recent years, due mainly to their intermediacy in a number of catalytic reactions,’ e.g. alkene metathesis,’ diene oli- gomerization3 telomerization of butadiene and car- bon dioxide,4 etc. In addition, use of cyclo- metallated compounds allows the study of some transformations of transition metal complexes which undergo facile decomposition reactions. Work by Whitesides and co-workers has dem- onstrated that for many such systems’ the p-hydro- gen elimination reaction can be suppressed by con- straining the M-C,-+-H dihedral angle to values far from the optimal 0”. Other metallacycles undergo decomposition by this well-known path- way, but their thermal stability is generally much

t Author to whom correspondence should he addressed.

higher than that displayed by their acyclic ana- logues.

We have reported recently6” the formation of the nickelacyclopentene complex [(Me,P),Nri(CH, mgH4)] (1). Many cyclometallated com- plexes of nickel are known7-lo and the simplest of the nickelacyclopentane units, Ni(CH2CH,CH2CH2), is known to undergo” three major decomposition pathways : B-hydrogen elimination, carbon- carbon bond cleavage to ethylene, and reductive elimination. Since the latter process is very often favoured in L,NiRR’ compounds (RR’ = alkyl or aryl groups) by addition of a phosphine or other ligand,12 we have attempted the elimina- tion of cyclobutene by addition to compound 1 of N- and P-containing ligands. Instead we have found that the nickelacyclopentene complex 1, [(Me,P)&i(CH,CMe,-o-&H4)], undergoes sub-

1070 E. CARMONA et al.

stitution of one of the two PMe, ligands. This sub- stitution chemistry is the subject of this paper, which describes also the results of a single-crystal X-ray structural determination, carried out with the mixed PMe3-py derivative, [(C,H,N)(Me3P) Ni(CHzCMez-o-&H,)] (2).

RESULTS AND DISCUSSION

We have recently shown that the cyclometallated complex 1 can be readily prepared by reacting [NiC12(PMe,),] with 2 equiv of Mg(CH&Me* Ph)Cl, in the presence of I- as a catalyst. Since this metallacyclic compound exhibits a very rich insertion chemistry, the synthesis of similar cyclic units, containing different co-ligands, has been undertaken.

An X-ray structural determination carried out on compound 1 has shown6b that, in spite of the different trans-influence of the alkyl and aryl groups, the two Ni-P bonds have nearly equal lengths. Both groups have good trans-directing properties and indeed the fluxional behaviour observed for 1 can be explained in terms of a fast intermolecular exchange between coordinated and traces of free PMe,. NMR data suggest the inter- change process to be faster for the PMe, ligand trans to the Ni-C(alky1) bond. On this basis, it is reasonable to expect facile substitution of one of the two PMe, ligands, with formation of new metal- lacycles. Since, on the other hand, cyclometallated 1 is stable towards reductive elimination of the organic fragment, even in the presence of added phosphine ligands, simple substitution reactions should provide access to the desired compounds. We have studied the interaction of 1 with two N-containing ligands, pyridine (py) and tmen (Me2NCH,CH2NMe,) and with two P-donors, PMe,Ph and dmpe (Me2PCH,CH2PMe2). Clean reactions are only observed for py and dmpe, while tmen fails to give the corresponding substitution product and the PMezPh derivative is best pre- pared by direct alkylation of [NiC12(PMe2Ph)J, as discussed below.

Reaction of 1 with pyridine. Formation of 2 and its molecular structure

Treatment of 1 with an excess of py at room temperature, affords, after work-up, a yellow crys- talline material of composition [(C,H,N)(Me3P) Ni(CHICMez-o-C,H,)] (2). The new complex has solubility and reactivity towards oxygen and mois- ture very similar to those of 1, but at variance with the behaviour found for the latter complex, it has rigid structure in solution. NMR data

strongly suggest that the py ligand is occupying the position tram with respect to the Ni-CH2 bond. In accord with this, the methylene carbon nucleus, Ni-CH2, gives rise to a doublet in the 13C{ ‘H) NMR spectrum, with a coupling constant,

2JCP of 13.7 Hz. In the related metallacyclobutene [(R3’P)Ni(CHZ-o-C6H4)],r3 values of ca 23 and 55 Hz are found for cis- and trans- ’ 3CH2-Ni-3 ‘P couplings, respectively. Formation of 2 can there- fore be represented as indicated in eq. (1). The reac-

PY G PMe3 (1)

1 2

tion can be readily reversed by addition of PMe, to solutions of 2. As already mentioned, the facile substitution of the ligand which is tram with respect to the Ni-alkyl bond is not unexpected and follows from the higher trans effect of this group, as com- pared with the aryl ligand. Note however, that this kinetic effect does not seem to be related to any appreciable weakening of the corresponding bond in the ground state of the molecule, since the Ni-P bonds in 1 have nearly equal lengths.6b

The geometry proposed for 2 on the basis of spectroscopic data has been confirmed by a single- crystal X-ray study. Figure 1 shows an ORTEP view of the molecule of 2 and Tables 1 and 2 include relevant structural data. The coordination around nickel is slightly distorted square-planar, with some distortion being imposed by the relatively small bite angle of the chelating organic ligand which constrains the C(l)--Ni-C(6) angle to 82.4(2)“. The remaining angles between pairs of cis-ligands are close to the ideal 90” value (Table 2). The square-planar arrangement is further emphasized by angles between trans-ligands, C(6)-Ni-P and C(l)-Ni-N of 172.4(2) and 175.2(2)“, respec- tively. The Ni-P distance is somewhat longer than the corresponding distance in 1(2.197( 1) vs 2.192(4) A), but the Ni-C(alky1) bond length of 1.935(5) A and the Ni-C(ary1) separation of 1.917(5) A, are slightly shorter than the corresponding values of 1.96(l) and 1.93(l) A, found respectively in the parent complex 1. These bond lengths are not excep- tional and fall in the range observed for other alkyl and aryl complexes of nickel(II).r4 The Ni-N sep- aration, 1.963(4) A, is close to the 1.957(8) A value reported for [Ni(CHzSiMe3)2(py)2], ’ 5 and appre- ciably smaller than the distance of ca 2.08 A observed in bis(pyridine) octahedral complexes of nickel(I1). ’ &’ ’

Fig. 1. ORTEP view of the molecule of 2.

1071

Table 1. Crystal and refinement data for 2

Empirical formula Crystal system Space group Cell dimensions

a (A) b (A) c (A) B (“)

Z

V(A’) Dcalc (g cm- ‘) Temperature (“C) Mol wt Linear absorption

coefficient (err- ‘) F(OOO) Crystal dimensions (mm) Diffractometer Radiation

Scan technique 20 range (“) Data collected Reflections collected Unique data Data with [I > 30(Z)] R int (%) Standard reflections Decay

K(F) (%) K,(F) (%) Average shift/error Data/parameter

C,8H2aNNi Monoclinic

~,/c

9.154(2) 10.810(2) 19.24(l) 102.30(2) 4 1860(l) 1.24 22 346.094 11.25

736 0.3 x 0.4 x 0.6 Enraf-Nonius CADCF Graphite monochromated

MO-K, (I = 0.7107 A) W20 l-50 (- lO,O,O) to (10,12,22) 3478 3367 2221 8.5 3 standards/ 111 reflections < 42% variation 4.5 5.0 0.0035 11

Reaction of 1 with the phosphine ligands, PMe,Ph and dmpc

Two synthetic routes can in principle be used for the preparation of the metallacyclic deriva- tives containing PMe,Ph and dmpe ligands: re- action of the chlorides, [NiC12P2] (P = PMe,Ph; P2 = dmpe), with an excess of the Grignard reagent, Mg(CH,CMe,Ph)Cl, in the presence of II, and sub- stitution of the PMe, ligands in 1 by the cor- responding phosphine. Rather interestingly, the PMe,Ph complex, [(PhMe,P)2Ni(CHzCMe2-o-C6 H4)] (3), can only be obtained in good yields by the first procedure, while formation of [(dmpe) Ni(CH2CMez-o-C,HJ] (4), is only accomplished by dmpe substitution of the PMe, groups in 1, eqs (2) and (3).

NiC1Z(PMe2Ph)z + 2Mg(CH&Me,Ph)Cla

(PhMe2P)&(CH2CMe2-u-C6H4)

+C,H&Me,+MgCl, (2)

(Me,P),Ni(CH,CMe,-o&H,) + dmpe ---+

(dmpe)Ni(CH,CMez-o-C31,H4)+2PMe3. (3)

Reaction (2) affords high yields of cyclometallated 3, which can be isolated as a yellow, moderately air- stable, crystalline solid. Its characterization as a metallacycle analogous to 1 follows from micro- analysis, and IR and NMR spectroscopy. As for the PMe, analogue, it is reasonable to assume6

1072 E. CARMONA et al.

Table 2. Selected bond distances (A) and angles (“) for 2

Ni-C( 1) 1.9353(59) N&C(6) 1.9167(54) Ni-N 1.9632(43) Ni-P 2.1974(19)

C(l)--C(2) 1.5238(85)

C(2)-cx3) 1.5145(79)

C(2)-~(4) 1.5441(86)

C(2)-C(5) 1.4994(74)

C(5)--c(6) 1.4166(72)

C(5)-C( 10) 1.3921(82)

C(6)-C(7) 1.4024(73)

C(7)-C(8) 1.3814(87)

N-Ni-P 94.30( 14) C(6)-Ni-P 172.39(17) C(6)--Ni-N 93.16(20) C( l)--Ni-P 90.22(18) C(l)--Ni-N 175.19(22) C(l)-Ni-C(6) 82.36(24) Ni-C(l)-C(2) 111.60(39)

C(l)-C(2)-~(5) 105.59(44)

C(l)-C(2)--c(4) 111.79(49)

C(lw(2)--c(3) 110.86(48)

C(4)_C(2)_C(5) 111.45(47)

C(3)-C(2k--C(5) 109.05(48)

C(3)-C(2FC(4) 108.09(51)

C(2)--C(5)--c(lO) 125.08(49)

C(2>-c(5)--c(6) 113.86(46)

C(6)_C(5)--c(lO) 121.06(50) Ni-C(6)-C(5) 115.46(38)

C(5F-C(6)--c(7) 116.11(48) Ni-C(6)-C(7) 128.43(41)

C(8>-c(9) 1.3707(93)

C(9)-C(lO) 1.3808(87) N-C(ll) 1.3254(71) N-C( 15) 1.3409(67) C(ll)--C(12) 1.3783(88) C(12)-C(13) 1.3704(90)

C(13)--c(l4) 1.3715(107) C(14)--C(15) 1.3690(93) P-C(l6) 1.8106(68) P-C(l7) 1.7971(59) P-C(l8) 1.8073(87)

C(6)_C(7)--c(8) 122.14(54)

C(7)---C(8yC(9) 120.59(57)

C(g)--C(9)-c(lO) 119.46(60)

C(5)--C( 1 OW(9) 120.56(55) Ni-N-C( 15) 123.30(36) Ni-N-C( 11) 118.25(35) C(ll)--N-C(l5) 118.43(48) N-C( 1 I)-C( 12) 122.90(49)

C(1 u--C(l2)--c(l3) 118.18(59) C(12)-C(13)---C(14) 119.38(62) c(13)--C(14)-c(15) 119.25(61) N--X(15)-C(14) 121.84(53) Ni-P-C( 18) 113.28(28) Ni-P-C( 17) 117.20(23) Ni-P-C( 16) 118.88(26) C(17)--P-X(18) 102.53(36) C(16)--P-C(l8) 102.01(37) C(16)-P-C(17) 100.50(34)

that the cyclometallation proceeds through an unstable dialkyl intermediate, [Ni(CH$Me,Ph), (PMe,Ph)J, which undergoes a rapid d-hydrogen abstraction reaction.

Complex 3 is fluxional ; the room temperature 31P{1H} NMR spectrum consists of two broad singlets centred at 4.3 and 0.2 ppm. Upon cooling, the spectrum somewhat narrows, but no coupling between the two anisochronous 31P nuclei can be observed, even at -80°C. These and other obser- vations suggest the existence of a phosphine-ex-

change process and, as for 1, the NMR spectra can be explained in terms of an exchange between coor- dinated and traces of free phosphine, by means of a five-coordinate intermediate species, as shown in Scheme 1. In the 13C{ ‘H} NMR spectrum, recorded at 20°C the two phosphine ligands give well- resolved doublets, and the Ni-CH2 resonance also appears as a doublet (2Jcp = 16 Hz), as a result of the coupling with only one of the 31P nuclei. These results contrast with those found for 1, whose room temperature 13C NMR spectrum exhibits a broad

3 * ( i) + PMelPh

Scheme 1.

(ii) PhMe2P\

- */N’ PhhIezP

5 0

3 (ii) - PMezPh

[(C,H,N)(Me,P)I?i(CH2CMe,-o-&H,)] 1073

signal for the two PMe, ligands and a singlet for the Ni-CH2 nucleus. It can therefore be concluded that the phosphine exchange process is faster for the PMe, derivative 1. The low value of 16 Hz found for 2Jcp is typical of a c&coupling (truns- 13C-13P coupling constants in complexes of this type have much higher values (ca 40-70 Hz), see refs 6 and 13 and the discussion of the NMR spec- tra of 4). This suggests that at this temperature the PMe,Ph ligand tram to the Ni-C(alkyl) bond is undergoing fast exchange with traces of free PMe,Ph via a phosphine association- dissociation process, while for the other coor- dinated phosphine ligand the rate of exchange is slow on the NMR time scale. These observa- tions are in agreement with the already men- tioned higher tram-effect of the alkyl group, as compared with the aryl ligand, and are also in accord with the behaviour reported for 1.6b Cooling to -50°C and below causes broadening of the Ni--cH2 resonance, but the expected doublet of doublets is not observed even at - 80°C.

As already indicated, complex 1 undergoes a smooth reaction with dmpe, with complete replace- ment of the PMe, ligands [eq. (311. The resulting compound 4 is a highly crystalline material, spar- ingly soluble in petroleum and diethyl ether, but readily soluble in other common organic solvents. As with the related metallacycles, 1-3, complex 4 displays high thermal stability, which contrasts with the propensity of complexes of the type [(dmpe) Ni(alkyl)(aryl)] to undergo reductive elimination reactions. ” The metallacyclic nature of l-4 is doubtless responsible for this enhanced stability.

In contrast with 1 and 3, and clearly due to the chelating nature of the dmpe ligand, 4 is a rigid molecule whose structure can be readily deduced from NMR studies. Thus, the 31P{ ‘H} NMR con- sists of an AX pattern (6,26.9,6x 34.8, 2J..,x 9 Hz), in accord with the existence of two different moieties in the metallacyclic unit. In the “C NMR spectrum, the methylene group gives rise to the expected doub- let of doublets, with tram and cis, 2Jcp, coupling constants of 65.8 and 18 Hz, respectively. Similar features are observed for the aromatic quaternary carbon bound to nickel, which also appears as a doublet of doublets.

As discussed above, complex 4 cannot be pre- pared by direct cyclometallation, but occurs by dmpe replacement of the PMe, ligands in 1. This is not surprising since the putative dialkyl inter- mediate, [(dmpe)Ni(CH2CMe2Ph)2], which can be obtained” by addition of dmpe to the unstable tmen derivative [Ni(CH,CMe,Ph)2(tmen)], ’ 5 does not metallate by moderate heating (6O”C, 4 days, toluene solution). These results are in accord with

those found previously by other workers2’ in related platinum systems and may be accounted for by reference to the chelating nature of the dmpe ligand.

EXPERIMENTAL

Microanalyses were carried out by the Pascher Microanalytical Laboratory, Bonn, and the Micro- analytical Service of the University of Sevilla. The spectroscopic instruments used were Perkin-Elmer models 557 and 684 for IR spectra and Varian XL- 200 for ‘H, 13C and 31P NMR spectra. All prep- arations and other operations were carried out under oxygen-free nitrogen, following conventional Schlenk techniques. Solvents were dried and degassed before use. The light petroleum used had b.p. 40-6O”C. Complex 1 was prepared according to ref. 6.

Synthesis of [(CgHsN)(Me3P)Ni(CH2CMe2-o-C6

WI (2)

0.34 g of complex l(1 mmol) were dissolved in 10 cm3 of Et,0 and to the resulting solution pyridine (2 cm3, excess) was added. The mixture was stirred for 2 h at room temperature, during which time it was occasionally exposed to vacuum to remove the replaced PMe, from the solution. The solvent was then pumped-off and the residue extracted with Et20 (25 cm”). Cooling at - 20°C furnished yellow- orange crystals of the desired compound (0.24 g, 70% yield). Found : C, 61.4 ; H, 7.6 ; N, 3.8. Calc. for CigH26NPNi: C, 62.5; H, 7.5; N, 4.0%. ‘H NMR (C6D6, 200 MHz): 6 0.63 (d, JHp = 6 Hz, PMe,), 1.48 (d, JHp = 11 Hz, Ni-CH*), 1.82 (s, CMe,), 6.31-7.29 (m, aromatics). 13C(‘H} NMR (C6D6): 6 13.1 (d, Jcp = 19 Hz, PMe,), 38.9 (d, Jcp = 14 Hz, Ni-CH2), 35.0 (s, CMeJ, 121.4, 123.4, 123.5, 134.3, 134.7, 150.7, 168.1 (aromatics). 31P(1H} NMR (C,D,) : 6 - 15.0 s.

Reaction of [(C,H,N)(Me,P)Ni(CH,CMe-o-C,HJ] (2) with PMe,

To a suspension of [(&H,N)(Me,P)Nm w,H,)] (2) (0.34 g, 1 mmol) in Et20 (10 cm3), PMe3 (0.5 cm3, 5 mmol, excess) was added and the mixture stirred at room temperature for 2 h. Evaporation of the solvent until a final volume of 2 cm3 and cooling at -20°C pro- vided 0.28 g of [(Me3P)2Ni(CH2CMe2-o-C6H4)].6 This crystalline material may sometimes contain small amounts of the unreacted pyridine derivative, that can be separated by fractional crystallization or additionally reacted with more PMe,.

1074 E. CARMONA et al.

Synthesis of [(PhMe,P),Ni(CH,CMe,-o-C,H3](3)

To a stirred suspension of [NiCl,(PMe,Ph)d (1.84 g, 4.5 mmol) in 60 cm3 of Et20, cooled to -30°C Mg(CH,CMe,Ph)Cl was added (7.2 cm3 of a 1.25 N solution in Et,O, 9 mmol). The mixture was stirred at low temperature for 15 min and then warmed and stirred at 30°C for an additional 3 h. The solvent was removed in vacua and the residue extracted with a petroleum etherdiethyl ether mixture (20 : 70 cm3). After centrifugation, con- centration to 30 cm3 and cooling at -20°C for 10 h, 1 g of the crude product was obtained. This material was purified by extraction with Et,0 and filtration. Partial evaporation of the solvent and cooling at - 30°C provided pure samples of the title compound as yellow needles (Yield 40%). Found : C, 67.01; H, 7.32. Calc. for C26H34PZNi : C, 66.85 ; H, 7.28%. ‘H NMR (C6D6, 200 MHz) : 6 0.99 (d, JHp = 15.8 Hz, P-Me), 1.84 (s, CMe,), 1.95 (d, JHp = 9.3 Hz, Ni-CH& 6.9-7.5 (m, aromatics). 13C{‘H} NMR (THF-CD3COCD3): 6 13.8 (d, Jcp = 22 Hz, PA--Me), 16.4 (d, Jcp = 21 Hz, P,-Me), 34.4 (s, CMe2), 50.8 (d, Jcp = 11 Hz, CMe2), 53.0 (d, Jcp = 16 Hz, Ni---CH& 119.9, 121.9, 122.2 and 138.4 (s, s, d, Jcp = 6 Hz, and s, nickelacycle CH aromatics), 167.0 (s, CAr--CMe2), 169.6 (d, Jcp = 79 Hz, Ni-C,,,,,ti,). 13P{ ‘H} NMR (THF-CD3COCD3) : 6 4.3 (s, PA), 0.2 (s, PB).

Preparation of [(dmpe)Ni(CH,CMe,-o-C6H4)] (4)

Complex 1 (0.64 g, 1.87 mmol) was dissolved in Et20 (15 cm3) and the solution cooled at -20°C. Dmpe (0.37 cm3, 1.87 mmol) was then added. After stirring at this temperature for a few minutes, a yellow crystalline product precipitated. The mixture was warmed and stirred at room temperature for 30 min, the solvent partially evaporated to half of the initial volume and the resulting suspension cooled to - 30°C and filtered. The title compound was obtained in almost quantitative yield. Recrys- tallization from Et20 provided yellow crystals of analytical purity. Found : C, 55.8 ; H, 8.2. Calc. for C,6H28P2Ni: C, 56.3; H, 8.2%. ‘H NMR (C6D6, 200 MHz) : 6 0.91 (d, JHp = 8 Hz, PA---Me), 1.01 (d, J = 7 Hz, P,-Me), 0.80-1.00 (m, P-CH2), 1.69 (s:CMe,), 1.88 (dd, JHp = 11 Hz, JHpB= 3 Hz, Ni-CH& 7.2-7.3 (m, ar>matics). 13C(lH} NMR (C,D,): 6 11.9 (d, Jcp = 22 Hz, PA--Me), 13.2 (d, Jcp = 15 Hz, P,Me), 27.1 (dd, JCPA = 25 Hz,

7 Supplementary material available. Tables of frac- tional coordinates, thermal parameters, bond distances and angles, and observed and calculated structure factors

Jcps = 20 Hz, P,--CH,), 28.6 (dd, JcpB = 27 Hz, JcpA = 21 Hz, PB-CH2), 35.8 (d, Jcp = 5 Hz, CMe,), 48.3 (dd, Jcp, = 66 Hz, Jcp, = 18 Hz, Ni-CH3, 51 .O (dd, JCPA = 9 Hz, Jcp, = 3 Hz, CMe,), 122.1, 122.2, 123.5 and 140.0 (s, s, s and dd, JCPA = 14 Hz, Jcp, = 4 Hz, CH aromatics), 167.3 (dd, Jcp, = 85 Hz, Jcp, = 14 Hz, Ni- C aromatic), 169.4 (d, JCP = 5 Hz, CAi--CMe2). “P(‘H} NMR (C,D,): 6 26.9 (d, PA), 34.8 (d, PB, Jpp = 9 Hz).

Structure solution and refinement

The crystal data and the parameters used during the collection and refinement of the diffraction data are summarized in Table 1. A yellow crystal was coated with an epoxy resin and mounted on the diffractometer. The cell dimensions were refined by a least-squares fit of the 8 values of 25 reflections. There was appreciable change in the periodically monitored standard reflections because the crystal became damaged by radiation. The intensities were corrected for decay and for Lorentz and polariz- ation effects.

Scattering factors for neutral atoms and anom- alous dispersion corrections for nickel and phos- phorus were taken from the International Tables for X-ray Crystallography. 22

The structure was solved by Patterson and Fourier methods, and an empirical absorption correction23 was applied at the end of the isotropic refinement.

The final refinement was made with anisotropic thermal motion for the non-hydrogen atoms and fixed isotropic temperature factors and calculated coordinates for hydrogen atoms.?

Most of the calculations were carried out with XRA Y80 system. 24

Acknowledgements-Generous support of this work by the Agencia National de Evaluacibn y Prospectiva is very gratefully acknowledged. M.P. thanks the Ministerio de Education y Ciencia for support by a research grant.

for 2 (26 pp.). 5. J. X. McDermott, J. F. White and G. M. Whitesides,

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[(CgH5N)(Me,P)Ni(CH,CMe,-o&H,)] 1075

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