1072
J . Am. Chem. SOC.1985, 107, 1072-1073
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Coupling of Acyl and Iminoacyl Groups on Zirconium and a2,a-Coordination of the Resulting Enamidolate Ligand Anne K . McMullen and Ian P. Rothwell* Department of Chemistry, Purdue University West Lafayette, Indiana 47907 John C. Huffman Molecular Structure Center, Indiana University Bloomington, Indiana 47405 Received November 13, 1984 The transition-metal-acyl group is a critical function in organometallic chemistry as its structure and reactivity determine the pathway that catalytic and stoichiometric cycles based on the migratory insertion of carbon monoxide into metal alkyl bonds can take.' For early d-block and actinide elements the reactivity of these functions is best accommodated into a bonding description in which an oxycarbene resonance makes a significiant contrib ~ t i o n . ~A, ~similar picture also exists for the less well-studied isoelectronic iminoacyl group. We wish to communicate here our initial findings on the products of migratory insertion of carbon monoxide and alkyl isocyanides into a series of zirconium-benzyl compounds containing the bulky ligand 2,6-di-tert-butylphenoxide (OAr'). This work demonstrates some novel reactivity and furthermore indicates a possibly general ground-state structural feature of simple heteroatom-substituted metallacylopentenes. The complex Zr(OAr'),(CH,Ph)j reacts readily with 2 equiv of alkyl isocyanide R N C (R = t-Bu; 2,6-dimethylphenyl) in hydrocarbon solvents to give almost quantitative yields of the bisinsertion products (2) (Scheme I).5 Intermediate, monoinsertion complexes were detected spectroscopically and in the case of the insertion of the more sterically demanding 2,6-xylyl ligand, the intermediate compound was also isolated (1b).6 All of the insertion products contain bands in their infrared spectra around 1560 cm-' assignable to $CN) of a t2imino-acyl f ~ n c t i o nwhile ,~~~ the iminoacyl carbon atom is observed to resonate between 6 235-250 in the I3C N M R spectra. A single-crystal X-ray diffraction study of the bis(iminoacy1) complex 2a was carried out and confirmed the t2bonding of the two groups.' Figure 1 shows an ORTEP view of the molecule emphasizing the central coordination sphere. Although formally six-coordinate, the complex is best described as pseudotetrahedral about the zirconium atom with each of the t2-iminoacyl groups occupying a single coordination site. The two iminoacyl groups are oriented parallel with each other in a head to tail fashion and also parallel with the 0-Zr-0 plane.* The Zr-C and Zr-N distances are essentially identical
(1) Ford, P. C., Ed.; American Chemical Society: Washington, DC, 1981; "Catalytic Activation of Carbon Monoxide"; ACS Symp. Ser. No. 152. (2) (a) Bercaw, J. E.; Wolczanski, P. T. Acc. Chem. Res. 1980,13, 121. (b) Manriquez, J. M.; McAlister, D. R.; Sanner, R. D.; Bercaw, J. E. J. Am. Chem. SOC.1978,100, 2716. (c) Erker, G. Acc. Chem. Res. 1984, 17, 103 and references therein. (3) Marks, T. J. Science (Washington, D.C.) 1982,217, 989. (4) Latesky, S.; McMullen, A. K.; Rothwell, I. P.; Huffman, J. C. Organometallics, in press. (5) All compounds gave satisfactory analytical data. IH NMR (200 MHz, C6D6) (21)6 4.30 (S, CHZPh), 0.96 (S, N-t-Bu), 1.50 (OC,H,-t-Bu), 6.8-7.3 (m. Ar), (2b)4.18 (s, CH2Ph), 1.80 (s, NC6H#e2), 1.40 (s, OC6H,-t-Bu2), 6.7-7.3 (m, Ar); "C NMR (50.3 MHz, C6Ds) (2a) 6 244.3 (t-BuNCCH,Ph), (2b)239.0 (C,H,NCCHIPh); IR (Nujol mull) s(CN) (2a) 1570, (2b) 1560 cm-'. (6) lb: 'H NMR (200 MHZ, C6D6) 6 3.19 (s, ZrCH,Ph), 3.97 (s, tBuNCCHPh), 1.69 (s, C6H3Me2NCCH2Ph),1.43 (s, OC6H3-t-Bu2),6.8-7.3 (m, aromatics); I3C NMR (50.3 MHZ, C6D6) 6 246.3 (C6H3Me2NCCH2Ph); IR (Nujol mull) s(CN) 1530 cm-l. (7) Crystal data for N, (2a)at -157 OC: space group C2/c, a = 23.612 (8) A, b = 11.198 (4) c = 21.243 (8) A, B = 123.52 (2)O, Z = 4, d,,, = 1.206 g ~ m - ~Of. the 3066 unique reflections collected by using Mo Ko!radiation, 6' 5 28 5 45', the 2665 with F > 3.00 o(F) were used in the full-matrix refinement. Final residuals are RF = 0.0345 and R,, = 0.0367.
A,
Figure 1. ORTEP view of Zr(OAr')2(t-BuNCCH2Ph)2 (2a). Important bond distances (A) and angles (deg): Zr(1)-O(2) = 2.027 (2); Zr(1)-N(17) = 2.221 (3); Zr(1)-C(18) = 2.228 (3);N(17)
