SYNTHESIS AND PROPERTIES OF 7-COORDINATE ISOCYANIDE COMPLEXES OF MOLYBDENUM(II) AND TUNGSTEN(II) CONTAINING CARBONYL AND TRIMETHYLPHOSPHINE LIGANDS - X-RAY STRUCTURE OF MOCL2(CNBUT)(CO)(PME3)3

The reaction of the seven-coordinate compounds MCl2(CO)2(PMe3)3 (M = Mo, W) with isocyanides (CNR) in the presence of PMe3 affords the monoisocyanide derivatives MCl2(CNR)(CO)(PMe3)3 (M = Mo, R = But (1a), Cy (1b), C6H5CH2 (1c), 2,6-C6H3Me2 (1d); M = W, R = But (2)). Complex 1a has been characterized by a single-crystal X-ray structural determination. The complex is monoclinic, space group P21/n, with a = 15.217 (4) Å, b = 16.367 (3) Å, c = 9.804 (2) Å, β = 90.75 (2)°, and Dcalcd = 1.38 g cm−3 for Z = 4. The bis(isocyanide) derivatives MCl2(CNBut)2(CO)(PMe3)2 (M = Mo (3), W (4)) may be isolated from the reaction of MCl2(CO)2(PMe3)3 with 2 equiv of CNBut, in the absence of added PMe3. These reactions proceed initially with substitution of a PMe3 ligand by CNR to produce the reactive intermediate species MCl2(CNR)(CO)2(PMe3)2 that could react further with either PMe3 or CNR (R = But) to afford compounds 1 and 2 or 3 and 4, respectively. Indeed, one such intermediate, WCl2(CNBut)(CO)2(PMe3)2 (5) has been isolated. Action of an excess of CNBut (>4 equiv) on the chlorocarbonyls MCl2(CO)2(PMe3)3 produces the electron-rich species [MCl(CNBut)4(PMe3)2]Cl (M = Mo (6), W (7)) that undergo reductive coupling of two isocyanide ligands, as demonstrated by the conversion of 6 into [MoCl(CNBut)2(But(H)NC≡CN(H)But)-(PMe3)2]Cl (8). On the other hand, compound 1a reacts with Mg(CH2CMe3)Br with formation of the η2-acyl MoBr(η2-COCH2CMe3)(CNBut)(PMe3)3 (9). © 1990, American Chemical Society. All rights reserved.