SYNTHESIS AND CHARACTERIZATION OF RE(VII) ALKYLIDENE ALKYLIDYNE COMPLEXES OF THE TYPE RE(CR')(CHR')(OR)2 AND RELATED SPECIES

A convenient one pot synthesis of Re(NAr)2(py)Cl3 consists of addition of excess trimethylchlorosilane, pyridine, and 2,6-dimethylaniline (ArNH2) to Re2O7 or [NH4] [ReO4] in dichloromethane. Re(N-2,6-C6H3-i-Pr2)2(py)Cl3 and Re(N-t-Bu)2Cl3 can be prepared similarly in high yield. Alkylation of these species with dineopentyl or dineophyl zinc or Grignard reagents affords complexes of the formula Re(NR)2(CHR')(CH2R') (R = 2,6-C6H3Me2, 2,6-C6H3-i-Pr2 or tert-butyl; R' = CMe3 or CMe2Ph). Treatment of Re(NR)2(CHR')(CH2R') complexes with an appropriate HCl source yields dimers of the general formula [Re(CR')(CHR')(RNH2)Cl2]2, which exist as a mixture of two isomers. An X-ray study of [Re(C-6-Bu)(CH-t-Bu)(ArNH2)Cl2]2 (a = 10.05 (1) angstrom, b = 21.65 (3) angstrom, c = 10.99 (1) angstrom, beta = 98.28 (9)-degrees, Z = 2, fw = 1031.08, rho(calcd) = 1.446 g/cm3, space group = P2(1)/n) showed it to contain two bridging halides with mutually cis alkylidene and alkylidyne ligands trans to the bridging halides. Several monomeric derivatives having the general formula Re(C-t-Bu)(CH-t-Bu)L2Cl2 (L = t-BuNH2, pyridine, 1/2TMEDA, 1/2phenylenediamine (pda)) were prepared, and related monoadducts, Re(c-t-Bu)-(CH-t-Bu)(L)Cl2, have been observed in solution. Treatment of Re(C-t-Bu)(CH-t-Bu)(pda)Cl2 with HCl(g) in dimethoxyethane affords air- and water-stable [Re(C-t-Bu)(CH-t-BU)Cl2]x (x > 1). An alternative route to [Re(C-1-Bu)(CH-t-BU)Cl2]x consists of treatment of Re(O)2(CH-t-Bu)(CH2-t-Bu) with HCl(g) in dimethoxyethane. Re(O)2(CH-t-Bu)(CH2-t-Bu) is prepared by the acid-catalyzed hydrolysis of Re(NAr)2(CH-t-Bu)(CH2-t-Bu) via intermediate Re(NAr)(O)(CH-t-Bu)(CH2-t-Bu). Re(NAr)2(CH-t-Bu)(CH2-t-Bu) and Re(O)2(CH-t-Bu)(CH2-t-Bu) conproportionate in solution to give Re(NAr)(O)(CH-t-Bu) (CH2-t-Bu). [Re(C-t-Bu)(CH-t-Bu)Cl2]x is a versatile precursor to a variety of bisalkoxide complexes of the general formula Re(C-t-Bu)(CH-t-Bu)(OR)2 (OR = O-t-Bu, OCMe2(CF3), OCMe(CF3)2, O-2,6-C6H3-i-Pr2, OSi(t-Bu)3). Syn and anti rotameric forms of the Re(C-t-Bu)(CH-t-Bu)(OR)2 complexes interconvert thermally or photochemically. In syn rotamers usually J(CH) = 120-135 Hz and in anti rotamers J(CH) = 157-184 Hz. An X-ray study of syn-Re(C-t-Bu)(CH-t-Bu)-[OCMe(CF3)2]2(THF) (a = 9.891 (1) angstrom, b = 17.543 (2) angstrom, c = 16.570 (2) angstrom, beta = 95.90 (2)-degrees, Z = 4, fw = 759.69, rho = 1.764 g/cm3, space group = P2(1)/n) showed it to have a structure approximately halfway between a face-capped tetrahedron (THF trans to the neopentylidyne ligand) and a trigonal bipyramid.