Metalcarbon multiple bonds: synthesis, structure, and electrochemistry of chromium aminocarbyne and phenylcarbyne complexes bearing phosphine or alkyl isonitrile ligands

Abstract

The synthesis, structure and cyclic voltammetry studies of neutral and cationic chromium carbyne complexes bearing phosphine or alkyl isonitrile ligands are reported. Treatment of cis-X(CO) 2(pic) 2CrCN iPr 2 (pic: 4-methylpyridine) ( 1a: X  Cl; 1b: X  Br) with two equivalents of PMe 3 and PMe 2Ph, or one equivalent of 1,2-bis(diphenylphosphino)ethatne (dppe) affords the aminocarbyne complexes cis-Cl(CO) 2(PMe 3) 2CrCN iPr 2 ( 2a). cis-Cl(CO) 3(dppe)CrCN iPr 2 ( 2b) and cis-Br(CO) 2(PMe 2Ph) 2CrCN 1Pr 2 ( 2e) respectively. In comparison, reaction of 1a with two equivalents of P(OMe) 3 gives selectively the trans-isomer Cl(CO) 2[P(OMe) 3] 2CrCN 1Pr 2 ( 3). Complex 2c is converted with TIPF 6 and PMe 2Ph to the cationic aminocarbyne complex [ fac-(PMe 2Ph) 3(CO) 2CrCN 1Pr 2][PF 6] ( 4). Similarly, the cationic phenylcarbyne complex [ fac-[ tBuNC) 3 (CO) 2CrCph][PF 6] ( 6a) is obtained from cis-Br(CO) 2( tBuNC) 2CrCPh ( 5a), TIPF 6 and tBuNC, Treatment of 1a with four equivalents of isopropyl isonitrile affords the cationic aminocarbyne complex [ cis-( iPrNC) 4(CO)CrCN iPr 2]Cl ( 9a), which is converted with TIPF 6 to [ cis-( iPrNC) 4(CO)CrCN iPr 2][PF 6] ( 9b). Comparative cyclic voltammetry studies of the aminocarbyne complexes 2a, 2c, 4, cis-Br(CO) 2( tBuNC) 2CrCN iPr 2 ( 5b), [ fac-( tBuNC) 3(CO) 2CrCN iPr 2][PF 6] ( 6b), mer-Br( tBuNC) 3(CO)CrCN iPr 2 ( 7), [ cis-( tBuNC) 4(CO)CrCN iPr 2][PF 6] ( 8b), [( tBuNC) 5CrCN iPr 2IPF 6] ( 10) and the phenylcarbyne complexes 5a and 6a are reported. The crystal structures of the aminocarbyne complexes 2a and 2c are described.