Tricarbonylchromium complexes of Me2ER2 ligands (E = C, Si, Ge, Sn, Pb; R = Ph, CH2Ph, p-tolyl)

Abstract

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.

Arenechromiumtricarbonyl complexes of silyl(germyl)(stannyl)- and silyl(germyl)(plumbyl)methanes including the unexpected formation of arenechromiumtricarbonyldimethylsilanol, (η6-C6H5)Cr(CO)3SiMe2OH

“…As expected the NMR spectra of the chromium complexes 4–6 exhibited an upfield displacement of chemical shifts of the aromatic protons and carbons of ~ 2 ppm and ~ 30–40 ppm, respectively [8,9]. No significant change in the chemical shifts for the 119 Sn and 207 Pb resonances of the arenechromiumtricarbonyl complexes 5 and 6 were observed compared to those of the precursors 2 and 3 .…”

“…The structure of compound 7 , Figure 1, exhibits the classical η 6 -arene-ML 3 form of a piano stool with a planar benzene ring seat lying symmetrically above the π-bonded chromium atom with the three carbonyl groups oriented in a tripod fashion in opposite direction to the benzene ring [8, 9]. The structural parameters and selected bond angles and distances are provided in Table 2 and Table 3.…”

Reversible Reactions of Ethylene with Distannynes Under Ambient Conditions

“…The Sn-Sn distance is increased to an average of 2.886( 6 The spectroscopic data for 3 and 4 support this picture. For example, the observed 2 J SnH coupling for 3 of 46 Hz is within the known range for Sn-CH 2 moieties, and the 1 H NMR chemical shifts of the CH 2 CH 2 hydrogens are in the alkane, rather than the alkene region (26)(27)(28). The 119 Sn NMR spectrum of 3 exhibits a singlet at 343 parts per million with 1 J119 Sn-117 Sn coupling of 3130 Hz.…”

Transition-Metal-Mediated Dearomatization Reactions

“…The preferred method for the synthesis of (arene)Cr(CO) 3 complexes is thermolysis of Cr(CO) 6 under an inert atmosphere (N 2 or Ar) in the presence of an excess of the arene in a high-boiling solvent. This can be the arene itself or a variety of solvent mixtures, − the most frequently adopted procedure is a mixture of the arene, dibutyl ether, and THF . This procedure is suited for the preparation of a wide range of complexes, often in high yields (80−95%) with reaction times typically in the 1−4 day range.…”