METAL-CARBON MULTIPLE BONDS - SYNTHESIS, STRUCTURE, AND ELECTROCHEMISTRY OF CHROMIUM AMINOCARBYNE AND PHENYLCARBYNE COMPLEXES BEARING PHOSPHINE OR ALKYL ISONITRILE LIGANDS

The synthesis, structure and cyclic voltammetry studies of neutral and cationic chromium carbyne complexes bearing phosphine or alkyl isonit rile Ligands are reported. Treatment of cis-X(CO)(2)(pic)(2)Cr=(CNPr2) -Pr-i (pic: 4-methylpyridine) (la: X = Cl; Ib: X = Pr) with two equiva lents of PMe3 and PMe2Ph, or one equivalent of 1,2-bis(diphenylphosphi no)ethane (dppe) affords the aminocarbyne complexes cis-Cl(CO)(2)(PMe3 )(2)Cr=(CNPr2)-Pr-i (2a), cis-Cl(CO)(2)(dppe)Cr=-(CNPr2)-Pr-i (2b) and cis-Br(CO)(2)(PMe2Ph)(2)Cr=(CNPr2)-Pr-i (2c) respectively. In compari son, reaction of la with two equivalents of P(OMe)(3) gives selectivel y the trans-isomer Cl(CO)(2)[P(OMe)(3)](2)Cr=(CNPr2)-Pr-i (3). Complex 2e is converted with TIPF6 and PMe2Ph to the cationic aminocarbyne co mplex [fac-(PMe2Ph)(3)(CO)(2)Cr=(CNPr2)-Pr-i][PF6] (4). Similarly, the cationic phenylcarbyne complex [fac-((BuNC)-Bu-t)(3)(CO)(2)Cr=CPh][PF 6] (6a) is obtained from cis-Br(CO)(2)((BuNC)-Bu-t)(2)Cr=CPh (5a), TlP F6 and (BuNC)-Bu-t. Treatment of la with four equivalents of isopropyl isonitrile affords the cationic aminocarbyne complex [cis-((PrNC)-Pr- i)(4)(CO)Cr=(CNPr2)-Pr-i]Cl (9a), which is converted with TIPF6 to [ci s-((PrNC)-Pr-i)(4)(CO)Cr=(CNPr2)-Pr-i][PF6] (9b). Comparative cyclic v oltammetry studies of the aminocarbyne complexes 2a, 2c, 4, cis-Br(CO) (2)((BuNC)-Bu-t)(2)Cr=(CNPr2)-Pr-i (5b), [fac-((BuNC)-Bu-t)(3)(CO)(2)C r=(CNPr2)-Pr-i][PF6] (6b), mer-Br((BuNC)-Bu-t)(3)(CO)Cr=(CNPr2)-Pr-i ( 7), [cis-((BuNC)-Bu-t)(4)(CO)Cr=(CNPr2)-Pr-i][PF6(8b), [((BuNC)-Bu-t)( 5)Cr=(CNPr2)-Pr-i][PF6] (10) and the phenylcarbyne complexes 5a and 6a are reported. The crystal structures of the aminocarbyne complexes 2a and 2e are described.