624wavelength (nm) H. halobium mutant (JW 5), and the Deutsche Forschungsgemeinschaft and the Fonds der Chemischene Industrie for financial support.

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Organometallics 1982,1, 851-858 851 encing chemistry of these complexes seems to be the most informative and internally consistent method of categorizing these and related compounds.The previous EHMO description of M(HCdH),(dtc); utilized a M-C(a1kyne) distance of 2.03 A and resulted in a calculated barrier to rotation of 40.3 kcal mol-'. The discrepancy between experimental (AG* of 15.3 kcal mol-') and calculated energy barriers for Mo(EtC,Et),(S,CNMez), was much larger than we had found in M(CO)(HC= CH) (dtc), and M(0) (HCECH) (dtc), studies. Although 2.03 A was the M-C distance reported for W(CO)(HC= CH)(det~),,~ structural data for (?r-C,H,)Nb(CO)(PhC= CPh);' and (7r-C5H5)WC1(CF3C4Y2F3)29 suggested that a distance of 2.17 A would be more likely to characterize the bis(alkyne) derivative. The results of such a calculation produced a barrier of 13.2 kcal mol-' for rotation of one alkyne, much nearer the observed value. The variation in calculated barrier as a function of the M-C distance (-2.0 kcal mol-'/O.Ol A) is consistent with a strong dependence of the metal-alkyne 7r-acceptor and a-donor orbital contributions on nuclear separation. Mono-and bis(arene)tricarbonylchromium complexes of (CH3)zE(C6H5)2[Cr(Co)3]x, where E = C, Si, Ge, Sn, and Pb, and (CH3)2Sn(CH2C6H5)2[Cr(C0)3]x and (CH3)zSn(C6H5CH3-p)2[Cr(CO)3]x, where x = 1 (1) (a) Bucknell University. (b) University of Oklahoma.(2) Poeth, T. P.; Harrison, P. G.; Long, T.

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Sterische und elektronische Einflüsse von Substituenten am Phenylring oder Einflüsse einer möglichen Koordination von Heteroatomen der Phenylsubstituenten am Sn(II)‐Atom auf die Stabilität von aus Aryl‐Li‐Verbindungen und Sn‐dichlorid gebildeten monomeren Aryl‐Sn(II)‐Produkten werden untersucht.