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 e 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.

Substituent effect in para substituted Cr(CO)5–pyridine complexes

“…Moreover, these compounds were found to exhibit non-linear optical properties [3]. Processes of displacement of coordinated N 2 by H 2 in unstable compounds using low-temperature/high-pressure techniques were also investigated for the M(CO) 5 -L (M = Cr, Mo, W) complexes [4]. The M(CO) 5 -L derivatives are the attractive model systems for many investigations carried out by means of quantum-chemistry modeling.…”

Activation of Molecular Hydrogen

“…Perhaps the most novel preparation was Poliakoff's photolysis of the hexacarbonyls impregnated in polyethylene disks under H 2 or N 2 pressures to give M(CO) 6Àn (L) n , where n ¼ 1-2 for L ¼ H 2 and 1-4 for N 2 . 161 Reactivity followed the order Mo > Cr > W, and H 2 can displace coordinated N 2 in the polyethylene media. W(CO) 5 (H 2 ) was both generated and dissociated in this and hypercrosslinked polymer matrices by UV photolysis at 220 and 90 K, respectively.…”

“…131,[160][161][162][163][164] In all media, vibrational spectroscopy provided the crucial evidence for H 2 rather than dihydride binding. The H--H, H--D, and D--D stretching modes are often observed because of the clear spectroscopic window in rare-gas media, although the experiments are decidedly much more difficult than routine IR or Raman spectroscopy.…”

Controlled Pyrolysis of Metal‐Containing Precursors as a Way for Synthesis of Metallopolymer Nanocomposites

“…By contrast, the similar ruthenium complex Ru(h 4 -C 8 H 10 )(h 6 -C 8 H 12 ) had decomposed slowly even at 0.3 MPa in the presence of PVP. The Mo, Cr, and W hexacarbonyls do not photochemically decompose at high pressures (~35 MPa) of N 2 or H 2 and low temperatures (~30 K) in polyethylene matrix but gave the different substituents only [109] as well as ferrum carbonyls in PE matrix at 190 K [110]. The nanoparticles of Ru (~1.2 nm) [111], Pd, and Pt [112,113] also can be produced from the organometallic precursors in PVP matrix at 298 K. Nickel dicyclo-octadiene Ni(COD) 2 can spontaneously decay (at room temperature in PVP dichloromethane solution), forming the particles with mean size 2-3 nm [114].…”