Organometallics 1986,5,1266-1268
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Where L = PEh,we observe reproducible reaction chemistry with the C-H and/or C-C bonds of acetonitrile and the tetra-n-butylammonium cation, depending upon the experimental conditions. A separate report will describe this chemistry in detail.lg
Acknowledgment. Thanks are expressed to the donors of the Petroleum Research Fund, administered by the American Chemical Society, for support of this work. We acknowledge generous loans of platinum metals from Johnson-Matthey, Inc., and Kigre, Inc. Registry NO.ck-[PtCl2(PPh3)2],15604-36-1; [PtOz(PPh&, 29894-57-3;[Pt(CO,)(PPh,)Z], 17030-86-3;OPPh3, 791-28-6; [Pt(PPh&I, 13517-35-6;[Pt(PEt,),], 66916-63-0;[Pt(dppe)], PhCrCPh, 101519-43-1;[Pt(PPh,)z(PhC=CPh)], 15308-61-9; 501-65-5;[Pt(PPh3)2(MeOOCC=CCOoMe)], 22853-55-0; MeOOCCGa
cI\ ..As.,, As' Ga ,', ,Gg As" As %I
As'
,As
%I
As*
Figure 2. Exchange of the endo- and exocyclic arsino groups.
increased somewhat with decreasing concentrations. When the temperature was raised from 22 to 97 "C, the 'H AB quartet collapsed to a broadened doublet which then approached coalescence with the singlet. Likewise, the 13Cmethyl peaks broadened and coalesced at 78 "C (Figure lb). This spectroscopic behavior was reversible, with the exception of the formation of a small amount of the above diarsine. These changes of 'H and 13Cspectra, when coupled with the dimeric molecular weight and the absence of other species in the spectra, can only be reconciled by rapid exchange of the endo- and exocyclic bis[ (trimethylsilyl)methyl]arsinogroups. Spectra simulated on this basis were in excellent agreement with the experimental data. A AG*of 17.0 f 0.0 kcal/mol for the 13Cexchange was obtained by line-shape analysis1oand was (9) Based on NMR, same peaks as in spectra of authentic samples of the arsine" and the diarsine. The diaraine was prepared by the reduction of (Me.SiCH3nAeC1"1B with zinc amaleam in refluxine methanol. Anal. Cdcd (Founajfor Cl.&As2Si4: C, 38:s (38.11); H, g.89 (8.61). NMFt 'H (80 MHz, CJAJ 6 0.75 and 0.61 [AB pattem (2Jm = 13.6), 8 H, CH2], 0.12 (8,sH, S i e a ) ; (22.5 MHz, C a d 8 10.2 (8, CHA 0.5 (8, SiMe3. (10) (a) The '$6 (75.429 MHz) Me3Si-resonances from spectra at il temperatures (304,309,314,319,325,330,349,350,351,352,an 365 K) were compared with the simulations from the modified DNhfR3lobprogram, using Av = 83.5 Hz and a natural line width of 1.0 Hz,and the rate constants (5, 5, 11, 14.5, 29, 35, 150, 170, 185, 195, and 500 8-l) were obtained. A plot and least-squares analysis of In (k/T)vs. 1 / T yielded a slope (m = -8295 h 218) and an intercept ( b = 22.98 0.66). The equations'0c AH* = -mR, AS*= R(b - 23.76), and AG* = AH* - T&S were used to obtain AH*(16.5 f 0.4 kcal/mol), AS* (-1.55 h 1.3 cal/(mol K)), and AG'. (b) B d ,G.; Kleier, D. A. The Computation of Complex Exchunge-Broadened NMR Spectra, Program 166, Quantum Chemistry Program Exchange, Indiana University, 1970; revised b y Bushweller, C. H.; Bhat, G.; Letendre. L. J.; Brunelle, J. A.; Bilofsky, H. S.; Ruben, H.; Templeton, D. H.; Zalkin, A. J. Am. Chem. SOC. 1975, 97, 65 and by: Caves, T., North Carolina State University. (c) Sandstrom, J. Dynamic NMR Spectroscopy; Academic: London, England, 1982.
*
Organometallics 1986,5, 1268-1269
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in agreement with the estimate derived from the coalescence temperature. l1 The IH exchange process between 22 and 57 "C could be simulated by using the same kinetic parameters, without invoking pyramidal inversion of the exocyclic arsenics. Evidently, the latter is not a significant process in this temperature range, despite the fact that the electropositive gallium might be expected to reduce the inversion barrier. The equivalency of the bis[ (trimethylsilyl)methyl]arsino groups can be achieved by associative or dissociative mechanisms. The associative mechanism is intuitively more attractive, involving an intermediate in which one or both gallium atoms assume a five-coordinate squarepyramidal configuration (Figure 2). There is ample precedent for five-coordinate gallium.', The dissociative mechanism requires cleavage of one endocyclic Ga-As bond and then reclosure of the ring in a trans-cis-trans equilibrium process. Dissociation into two monomers is considered energetically improbable.
Acknowledgment. The financial support of this work by the Office of Naval Research is gratefully acknowledged. The technical contributions of R. Ernest and C. Foley (Duke University) and T. Caves (North Carolina State University) are similarly recognized. Registry No. (Me3SiCH2)2AsSiMe3, 101860-04-2; Me3SiC1,75-77-4;Me&SiMe3, (Me3SiCH2)2AaH, 101860-05-3; 101860-06-4;MesMgBr,2633-66-1; AsC13,7784-34-1; MekAsC1, 101860-07-5;Mes2AsH,101860-08-6;MeszAsLi,101860-09-7; [(MeSSiCH2)2AsGaC12]3, 101836-83-3;GaC13, 13450-90-3; ([(Me3SiCH2)2As]2GaC1)2, 101860-10-0;(Mes2AsGaC12),, 10183685-5;[(Me~~As)~GaCll,, 101836-87-7; (Me13~As)~Ga, 60607-12-7; Ph2AsH,829-83-4;(Me3SiCH2)3Ga, 72708-53-3;[(Ph2AsGa(CH2SiMe3)2],, 101836-89-9;Ph2AsAsPh2,2215-36-3;Me3Ga, 1445-79-0; (Ph2AsGaMe3),,101836-90-2. (11) AG,' = 17.0 i 0.1 kd/mol; obtained (in cal/mol) from the equation AGc* = T,[45.67 4.58 log (TJAv)],where T,= 351 i 1 K and Av = 83.3 i 0.2 Hz. (12) See, for example: (a) Pattison, I.; Wade K. J. Chem. SOC. A 1968, 2618. (b) Dymock, K.; Palenik, G. J. J. Chem. SOC.,Chem. Commun. 1973,884. (c) Rettig, S.J.; Storr,A.; Trotter, J. Can. J. Chem. 1976,53, 753. (d) Rettig, S. J.; Storr, A.; Trotter, J. Can. J. Chem. 1976,54,1278. (e) McPhail, A. T.; Miller, R. W.; Pitt, C. G.; Gupta, G.; Srivaetava, S. C. J. Chem. SOC., Dalton Trans. 1976, 1657. (13) Seyferth, D. U.S. Patent 2 964 550, 1960.
Figure 1. The molecular structure of [Cr(s3-C3H6)2(s5-C,Hd] (2).
In continuation of our investigation into the chemistry of the q3-allyl complexes of Cr, Mo, and W,,s3 we report here the preparation of the title compound and some representative reactions. It has previously been reported4 that [CrCl2(q5-C5H5)I5 reacts with dylmagnesium chloride in THF at room temperature to give a black binuclear species, [Cr(q3C3H6)(q5:C6).f5)],,(l),in low yield. The presumed intermediate m thu reaction [Cr(q3-C,H5),(q5-C~5)] (2) can be isolated in ca. 75% yield by carrying out the reaction a t -60 " in diethyl ether. 2 is an orange-yellow, paramagnetic
+
[Cr( 773-CgH5)2( v5-C5H5)]: Preparatlon, Structure, and Reactions K. Angermund, A. Whrlng, P. W. Jolly,' C. Kriiger, and C. C. Romlo' Max-Pknck- Institut fur Kohknforschung D-4330 Mtheim a.d. Ruhr, West Germany Received February 3, 7986
Summary: The title compound has been prepared by reacting [CrCl,(v5-C5H,)] with allyknagnesium chloride at -30 OC and the crystal structure determined by X-ray diffraction. Reaction with a variety of donor ligands is accompanied by reductive coupling of the allyl groups to give [Cr(L)(g2,v2-1,5-CsH,,)(v5-C,H5)] complexes while treatment with butadiene or alkynes leads to their displacement and the formation of mono- and binuclear Cr(v5-C5H5)species. (1) Present address: Instituto Superior Tecnico, Lisbaa, Portugal.
0276-7333/86/2305-1268$01.50/0
2
1
compound6 which reacts further in solution above ca. -10 "C to give 1.' The crystal structure of 2 has been determined by X-ray diffraction (Figure 1)8 and should be compared with that of the related molybdenum compound [Mo(q3-C3H5),(q5-C5H6)] The organic ligands are arranged in an essentially trigonal-planar geometry about the central metal atom with an angle of ca. 156" between the two allyl planes. Cr is smaller than Mo (covalent radius: Cr(O), 1.15 A; Mo(O), 1.31A), and as a result the
.,
(2) Jolly, P. W.; m e r , C.; RomHo, C. C.; Romb, M. J. Organometallics 1984,3, 936. (3) Benn, R.; Holle, S.;Jolly, P. W.; m e r , C.; Romao, C. C.; Romb, M. J.: Rufiieka. A.: Schroth. G. Polvhedron 1986.5.461. (4) Nieman, J.; Pattiasina;J. W.; 'keuben, J. H. J. brganomet. Chem. 1984,262, 157. (5) Prepared by reacting [Cr(q6-C6H6)a] with HCl(9) in pentane at 0 "C lvield 95%):see also: Klocke. H. J. Dissertation Ruhr-Universitiit Bochm, 1984. ' (6) Anal. Found (Calcd): Cr, 26.02 (26.10);C, 66.24 (66.31);H, 7.60 (7.54). M S m/e 199 (M+). Paramagnetic: 1.8 fig. (7) Anal. Found (Calcd): Cr, 32.79 (32.87);C, 60.89 (60.79);H, 6.26 Paramagnetic: 4.1 fig. (6.37). M S m/e 316 (M+). (8) X-ray diffraction data for CIIH16Cr(2): orange; crystal size (mm) 0.04 X 0.42 X 0.59; crystal system monoclinic; apace group ml/a(no. 14); a = 11.165 (4) A, b = 7.154 (2) A, c = 12.211 (2) A, 6 = 102.40 (2P; V = 952.6 A3; z = 4; d= 1.39 g/cm+; p(MoKn) = 11.14 cm-I; empirid absorption correction (0.890~-1.243,&; F(OO0)= 420, Enraf-Nonius CAD-4 diffractometer; graphite-monochromated Mo radiation (A = 0.71069 A); Zr Filter; can mode &2& T = 100 K; e range 1.7-27.3'; measured reflections 4317 (+h,ik,+l); unique reflections 2159, observed reflections 1779 (I Z 2aQ); atructure solved by heavy-atom method; hydrogen positions located and refined isotropidy; number of variables 169; R = 0.030, R = 0.038 (w = l&F&); EOF = 2.1; residual electron density = 0.55 e A-3. (9) Shannon, R. D. Acta Crystallogr.,Sect. A: Cryst. Phys., Diffr., Theor. Gen. Crystallogr. 1976, A32, 751.
0 1986 American Chemical Society
