Chemistry of Reactive Organometallic Compounds at Low Temperatures and High Pressures:  Reactions of M(CO)₆(M = Cr, Mo, W), (η⁶-C₆H₃Me₃)M(CO)₃(M = Cr and Mo), and W(CO)₅CS with H₂and N₂in Polyethylene Matrices

Abstract

An unusual high-pressure (<5000 psi) and low-temperature (>30 K) cell is used to study the photochemistry of d 6 metal carbonyl complexes and related compounds in a polyethylene (PE) matrix. This approach combines some of the advantages of traditional matrix isolation with those of low temperature solvents (e.g. liquid Xe). UV photolysis of M(CO) 6 under pressures of N 2 lead initially to the formation of M(CO) 5 N 2 and, on longer photolysis, to more highly substituted M(CO) 6- n (N 2 ) n ( n ≤ 4) species. Photolysis under a pressure of H 2 leads to M(CO) 5 (η 2 -H 2 ) and cis -M(CO) 4 (η 2 -H 2 ) 2, disubstituted compounds which were previously unknown for Mo and W. The thermal reactivities of all of these compounds were qualitatively established by raising the temperature of the PE matrix and monitoring the reaction with CO. The UV photolysis of W(CO) 5 CS and (η 6 -C 6 H 3 (CH 3 ) 3 )M(CO) 3 (M = Cr and Mo) also leads to previously uncharacterized H 2 and N 2 complexes. The low-temperature, high-pressure (LT−HP) cell allows gases to be exchanged during the course of a single experiment. The conditions needed for H 2 and N 2 to penetrate the PE and to be removed from it have been investigated, and this information has been used to study thermal exchange reactions between coordinated N 2 and η 2 -H 2 ligands in M(CO) 5 L compounds. It was found that the reactivity followed the order Mo > Cr > W.