Synthesis, spectroscopic and structural studies on transition metal carbonyl complexes of cyclic di- and tetra-selenoether ligands

Abstract

Reaction of [M(CO)4(nbd)] (M = Cr or Mo, nbd = norbornadiene) or [W(CO)4(TMPA)] (TMPA = N,N,N′,N′-tetramethyl-1,3-propanediamine) with [8]aneSe2 (1,5-diselenacyclooctane) yielded the cis-disubstituted tetracarbonyl species [M(CO)4([8]aneSe2)] (M=Cr, Mo or W). The complexes [M′X(CO)5] (M′=Mn, X=Cl, Br or I; M′=Re, X= Cl or Br) reacted similarly with [8]aneSe2 to give fac-[M′X(CO)3([8]aneSe2)] in high yield. Infrared and multinuclear NMR spectroscopic studies confirmed these assignments and indicated a single species in solution; δ(55Mn) lies in the same range as observed for other fac-[MnX(CO)3(diselenoether)] complexes, while for all of the compounds δ(77Se) is to low frequency of [8]aneSe2 itself (δ 137). Crystal structures of [W(CO)4([8]aneSe2)], [MnBr(CO)3([8]aneSe2)] and [ReBr(CO)3([8]aneSe2)] show the cyclic diselenoether chelating and adopting a chair-boat conformation. The compounds [16]aneSe4 (1,5,9,13-tetraselenacyclohexadecane) and L (1,6-diselena-3,4-benzocyclononane) reacted with the metal(II) species [{MoBr2(CO)4)}2] or [MI2(CO)3(NCMe)2] in CH2Cl2 solution to give seven-co-ordinate [{MoX2(CO)3}2([16]aneSe4)], [WI2(CO)3([16]aneSe4)], [MoX2(CO)3(L)] and [WI2(CO)3(L)], although these species decompose rapidly in co-ordinating solvents. Reaction of [16]aneSe4 with two molar equivalents of [M′Cl(CO)5] yielded the dinuclear complex [{MnCl(CO)3}2([16]aneSe4)] (in which the tetraselenoether is thought to bind in a bidentate manner to each Mn) and the mononuclear complex [ReCl(CO)3([16]aneSe4)] (which is thought to involve bidentate ligation to [16]aneSe4 with two free Se donors). The cationic species fac-[Mn(CO)3(η3-[16]aneSe4)]CF3SO3 was generated by treatment of [MnCl(CO)5] with AgCF3SO3 in Me2CO followed by addition of [16]aneSe4.