No CH activation of benzene, but a selective CSi activation of tetramethylsilane (TMS) characterizes the reactivity of the coordinative and electronically highly saturated, “hot” Pt0‐complex 2, which is formed from the cis‐hydridoneopentyl complex 1 at room temperature by elimination of neopentane. 2 can be detected by trapping reactions; reaction with TMS at room temperature leads quantitatively to the methyl(trimethylsilyl)‐complex 3, which is also formed by intramolecular rearrangement of the independently synthesized hydride complex 4.
The dinuclear chromium(II1) half-sandwich molecules [Cp* CrX 2] 2 (Cp* = C,Me,; X = Cl (l), Br (2), I (3)) and [CpCrX,], (Cp = C,H,; X = Br,
The introduction of a methyl substituent in the 2-position of 8-oxy-quinoline strongly alters its ligand properties in the complex formation with gallium(III). From aqueous solutions (ammonium acetate buffer, acetic acid, gallium nitrate) a pale-green complex (2-MeOx)2GaOAc is precipitated instead of the tris(oxinate) chelate. According to a single crystal X-ray diffraction study, the gallium atom is pentacoordinate in this complex, with two chelating 2-MeOx and one monocoordinate acetate ligands. Similar acetato complexes were generated with equally hindered 2,4-dimethyl- and 2,5,7-trimethylquinoline, as well as with 2-ethyl- and 2-n-propylquinoline ligands. Retaining the 2-MeOx ligand, acetate OAc could be exchanged for trifluoroacetate, propionate, cyanoacetate, and (in binuclear complexes) equivalents of succinic, maleic, fumaric, and acetylenedicarboxylic acid. From this series, crystal and molecular structures have also been determined for (2-MeOx)2GaOC(O)CH2CN and [(2-MeOx)2GaOC(O)CHJ2]2 (with crystal nitrobenzene). In the cyanoacetate, the nitrile function is not involved in intra/intermolecular metal coordination. In the binuclear succinate the molecule has a crystallographical center of inversion. As in the cyanoacetate, the environment of the two equivalent gallium centers of the succinate is very similar to that of the acetate complex.
Summery: The organoaluminum complex Ai [ o -(PhpCH,)C6H413 (Ph = phenyl) is obtained from AC13 and the Hthiated ligand in diethyl ether. As shown by 27AI NMR spectroscopy, it exhibits a pentacoordinate aluminum center (B(27AI) = 131 ppm, w,,, = 12 kHz). An X-ray structure analysis reveals a trigonal-bipyramldai coordination at aluminum wlth a donor set comprised of three carbon atoms in the equatorial plane and two of the three phosphino functions in axial positions with exceedingly (toluene), triclinic, space group fi (No. 2), a = 12.482 (2) A, b = 16.137 (3) A, c = 17.144 (2) A, a = 62.61 (I)", @ = 88.08 (1)O, y = 67.28 (1)O, V = 2784.0 As, R (R,) = 0.094 (0.091), w = l/a2(F,) for 463 refined paramaters). The coordination geometry is achieved by two of the anionic phosphines acting as chelating ligands, spanning equatorlei (C atom) and axial s k (P atom), while the third phosphine is only carbon-bonded.Ai[o-(Ph,PCH,)C,H,,] 3 is the first triorganoaluminum bis(phosphine) adduct where C3P2 pentacoordination at aluminum has been definitely proven for both the solution and the solid state.long Ai-P bonds (2.676 (3)/2.782 (2) A; C,7H,AIPa*1.25-Neutral pentacoordinate aluminum donor adducts of the type AlX3L2 (L = Lewis base; X = halogen, alkyl, hydrogen) are well established with donors containing "hard" donor sites, particularly n i t r~g e n .~~~ Well-characterized bis(phosphine) adducts seem to be limited to AlC13-(PMe3)2.4 Recently also stable 1:2 alane-phosphine adducts could be described for the first timeq5 Fivefold coordination in triorganoaluminum phosphine adducts has been claimed for 1:l diphosphine adducts: but recent evidence obtained on Ph2PCH2PPh2(AlMe3) only points to a highly fluxional molecule in solution with tetracoordinate aluminum even at -80 OC. 'In contrast to neutral phosphines, anionic phosphines have been shown to be good phosphorus ligands even to p-block metals.8 Phosphinomethanides, where the carbanionic function is directly connected to the phosphino group, have been successfully employed for this purpose and show a rich and varied coordination chemistry to main-group metals? Far less is known about the com-(2) Cotton, F. A.; Wilkinson, G. Adoanced Inorganic Chemistry, 5th (3) Miiller, G.; Krtiger, C . Acta Crystallogr. Sect. C 1984,40,628 and (4) Beattie, I. R.; Ozin, G. A. J. Chem. SOC. A 1968, 2373. (5) Bennett, F. R.; Elms, F. M.; Gardiner, M. G.; Koutaantonis, G. A,; Raston, C. L.; Roberta, N. K. Organometallics 1992,11, 1457. (6) Clemens, D. F.; Sieler, H. H.; Brey, W. S. Znorg. Chem. 1966,5,527. (7) Schmidbaur, H.; LauteschlMer, S.; Miiller, G. J. Organomet. Chem. 1986,281, 25. (8) Engelhardt, L. M.; Harrowfield, J. M.; Lappert, M. F.; McKmon, I. A.; Newton, B. H.; Raston, C. L.; Skelton, B. W.; White, A. H. J. Chem. Soc., Chem. Commun. 1986,846. ed.; Wiley: New York, 1988; pp 219, 226. references therein. Chart I R' ,C PR, ' --B (R = Ph, Me)A plexation behavior of anionic phosphines of type A toward main-group elements (Chart I).l0J1 In A the carbanionic function is not directl...
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