Conformations of cyclic compounds in solution. V. Nuclear magnetic resonance study of the conformational preferences of some substituted ditertiary arsine chelate complexes of chromium carbonyl

Abstract

L may be. That is, the intrinsically strong Mo-Mo bond necessitates an intrinsically weak Mo-L bond. This "metal-metal trans effect" operates to some extent in the other dinuclear carboxylates. Thus, in Cr2-(0Ac)4(H20)2s and Cr30(0Ac)6(H20)3+,28 the average Cr-OAc distances of 2.018 (2) and 1.98 (1) A are comparable to each other and to the Cr-OH2 distance in the trimer, 2.02 (1) A, but all are significantly shorter than the Cr-OH2 distance in the dimer, 2.272 (3) A. In the dimer, the water molecule is trans to the Cr-Cr bond; in the trimer, to the Cr-0 bond. Again, the Rh-OH2 distance of 2.310 (3) A in Rh2(OAc)4(H20)2 is substantially greater than the average Rh-OAc distance of 2.039 (2) A. Nowhere is the trans effect more dramatically illustrated than in the molybdenum system, however; therefore, Mo(II) appears to have an intrinsically greater metal-metal bonding tendency in the carboxylate framework than do Cr(II) and Rh(II). This has long been suggested from theoretical considerations and the available X-ray data,7 but never so conclusively demonstrated. One expects, then, that if good crystals of unsolvated M2(02CCF3)4, M = Cr, Rh, could be obtained, which may not be possible, the Cr-Cr and Rh-Rh distances would definitely be longer than the Mo-Mo distance in Mo2(02CCF3)4, allowing for differences in covalent radii. Moreover, if crystalline M2(02CCF3)4(py)2, M = Cr, Rh, could be obtained, which should be possible, the metal-nitrogen distances should definitely be shorter than in Mo2-(02CCF3)4(py)2, again allowing for differences in covalent radii. The lengths found for metal-to-axial ligand bonds in the carboxylates thus provide valuable information about the implicit tendencies of the metals toward mutual attraction.

Synthesis and characterization of (Me3Si)2AsCH2RCH2As(SiMe3)2 (R = CH2, SiME2) and

“…AsMe2 ( n = 1, 5), Me(C1)As(CH2),As(C1)Me (n = 2, 3) [14], and (Me3Si)2AsCH2As(SiMe3)2 [8]. Other methods of making bisarsines have included the reaction of acetyl chloride, ASzO3, and A1C13 to make C12AsCH2AsC12 [ 16,171, the synthesis of (HO)(0)(Ph)AsCH2CH2-As(Ph)(O)(OH) from ethylene bromide and phenyldichloroarsine in aqueous NaOH [18,191, and interestingly the insertion of vinyl fluoride into the As-As bond of tetramethyldiarsine to make Me2AsCH2CHFAsMe2 [20]. Curiously, though, the attempted preparation of (Me3Si)2AsCH2CH2As-(SiMe3)2 and Ph2As-CH2CH2AsPh2 using ethylene bromide and L~A S ( S~M~~)~-~T H F or KAsPh2, respectively, yielded ethylene deinsertion products of the type R2As-AsR2 [8, 151, even though formal ethylene deinsertion probably did not occur since it is believed that the desired products were not obtained even transiently.…”

Variable Temperature Nuclear Magnetic Resonance Studies of Some Five-Membered Ring Chelate Complexes

“…spectra of 1-9 are summarized in Tables 2 and 3, respectively. Specific details of the spectral analysis of these derivatives have been presented elsewhere (1)(2)(3)(4).…”

The Preparation of cis-1,3-Bis (dimethylarsino)-2,2,4,4-tetramethylcyclobutane and its Group VIB Metal Carbonyl Derivatives

“…The photolytic addition of tetramethyldiarsine to acetylenic and olefinic compounds has been useful for the preparation of ditertiary arsine ligands (1,2).…”