Synthesis of 2,2′,5,5′-Tetraphenyl-1,1′-diarsacalcocene and -strontocene

Abstract

The metalation of H2As−SiiPr3 with bis(tetrahydrofuran-O)calcium- and -strontium bis[bis(trimethylsilyl)amide] yields tetrakis(tetrahydrofuran-O)calcium- (1a) and -strontium bis(triisopropylsilylarsanide) (2a). These compounds are in equilibrium with their dimers 1b (Ca) and 2b (Sr) by elimination of THF. The addition of diphenylbutadiyne to a THF/toluene solution of 1 and 2 gives bis(tetrahydrofuran-O)calcium- (3) and -strontium bis(2,5-diphenylarsolide) (4). The proposed reaction mechanism explains the formation of the (iPr3Si)2As− and 2,5-diphenyl-3,4-bis(phenylethynyl)arsolide anions based on an intermolecular H/SiiPr3 exchange reaction. The latter anion was characterized by X-ray crystallography with the binuclear cation [(THF)3Ca{µ-As(H)SiiPr3}3Ca(THF)3]+ (5). The arsolide ligands of 3 and 4 are η5-bonded to the metal centers, whereas 5 crystallizes as a solvent-separated ion pair.