Synthesis,Structure,and Bridge-Terminal Exchange Kinetics of Pyrazolate-Bridged Digallium and Diindium Complexes Containing Bridging Phenyl Groups

摘要

Treatment of triphenylgallium with 3,5-dimethylpyrazole,3,5-diphenylpyrazole,or 3,5-di-tert-butylpyrazole in a 2:1 stoichiometry afforded the phenyl-bridged complexes (C_6H_5)_2-Ga(mu-Me_2pz)(mu-C_6H_5)Ga(C_6H_5)_2 (62%),(C_6H_5)_2Ga(mu-Ph_2pz)(mu-C_6H_5)Ga(C_6H_5)_2 centre dot C_7H_8 (62%),and (C_6H_5)_2Ga(mu-tBu_2pz)(mu-C_6H_5)Ga(C_6H_5)_2 (40%),respectively,as colorless or off-white crystalline solids.Treatment of triphenylindium with 3,5-di-tert-butylpyrazole in a 2:1 stoichiometry afforded the phenyl-bridged complex (C_6H_5)_2In(mu-tBu_2pz)(mu-C_6H_5)In(C_6H_5)_2 centre dot (C_6H_(14))_(0.5) (40%).The molecular structures of (C_6H_5)_2Ga(mu-Ph_2pz)(mu-C_6H_5)Ga(C_6H_5)_2 centre dot C_7H_8,(C_6H_5)_2Ga(mu-tBu_2-pz)(mu-C_6H_5)Ga(C_6H_5)_2 centre dot (C_6H_(14))_(0.5),and (C_6H_5)_2In(mu-tBu_2pz)(mu-C_6H_5)In(C_6H_5)_2 centre dot (C_6H_(14))_(0.5) consist of a 3,5-disubstituted pyrazolato ligand with a diphenylgallio or diphenylindio group bonded to each nitrogen atom.A phenyl group acts as a bridge between the two metal atoms.By contrast,treatment of triphenylgallium with 3,5-di-tert-butylpyrazole in a 1:1 stoichiometry or triphenylindium with 3,5-diphenylpyrazole or 3,5-dimethylpyrazole in 2:1 or 1:1 stoichiometry afforded the dimeric complexes [(C_6H_5)_2Ga(mu-tBu_2pz)]_2 (63%),[(C_6H_5)_2In(mu-Ph_2pz)]_2 (40%),and [(C_6H_5)_2In(mu-Me_2pz)]_2 (92%),respectively,as colorless crystalline solids.The dimeric nature of these complexes was determined by X-ray crystallography.Treatment of 3,5-di-tert-butylpyrazole with excess trimethylgallium afforded the dimeric complex [Me_2-Ga(mu-tBu_2pz)]_2 (82%) as the major product and Me_2Ga(mu-tBu_2pz)(mu-OCH_3)GaMe_2 (2.6%) as a minor product.There was no evidence for the formation of the methyl-bridged complex Me_2-Ga(mu-tBu_2pz)(mu-CH_3)GaMe_2.The kinetics of bridge-terminal phenyl exchange in (C_6H_5)_2Ga-(mu-Me_2pz)(mu-C_6H_5)Ga(C_6H_5)_2,(C_6H_5)_2Ga(mu-Ph_2pz)(mu-C_6H_5)Ga(C_6H_5)_2 centre dot C_7H_8,(C_6H_5)_2Ga(mu-tBu_2-pz)(mu-C_6H_5)Ga(C_6H_5)_2,and (C_6H_5)_2In(mu-tBu_2pz)(mu-C_6H_5)In(C_6H_5)_2 centre dot (C_6H_(14)_(0.5) was determined by ~(13)C NMR spectroscopy and afforded the following range of activation parameters: DELTA H~(not=) = 6.0-8.9 kcal/mol,DELTA S~(not =) = -23.1 to -32.0 eu,and DELTA G~(not =)_((298 K)) = 15.5-15.8 kcal/mol.The large,negative values of DELTA S~(not =) imply ordered transition states relative to the ground state and rotation along the N-GaPh_3 or N-InPh_3 vector without metal-nitrogen bond cleavage.The combined results suggest that the close proximity of the metal atoms is the principal determinant of the bridging phenyl interactions and that complexes of the heavier group 13 elements with bridging hydrocarbon ligands are likely to be more accessible than the current state of literature would suggest.