Synthesis, structure, properties, volatility, and thermal stability of molybdenum(II) and tungsten(II) complexes containing allyl, carbonyl, and pyrazolate or amidinate ligands

Abstract

Treatment of M(allyl)(Cl)(CO) 2(py) 2 (M = Mo, W) with 1 equiv. of potassium pyrazolates in tetrahydrofuran at −78 °C afforded M(allyl)(R 2pz)(CO) 2(py) n (R 2pz = 3,5-disubstituted pyrazolate; n = 1, 2) in 68–81% yields. X-ray crystal structure analyses of Mo(allyl)((CF 3) 2pz)(CO) 2(py) 2 and W(allyl)(tBu 2pz)(CO) 2(py) revealed η 1- and η 2-coordination of the (CF 3) 2pz and tBu 2pz ligands, respectively. Analogous treatment of Mo(allyl)(Cl)(CO) 2(NCCH 3) 2 with 1 equiv. of tBu 2pzK in tetrahydrofuran at −78 °C afforded [Mo(allyl)(tBu 2pz)(CO) 2] 2 in 79% yield. An X-ray crystal structure analysis of [Mo(allyl)(tBu 2pz)(CO) 2] 2 showed a dimeric structure bridged by two μ-η 2:η 1-tBu 2pz ligands. Treatment of M(allyl)(Cl)(CO) 2(py) 2 with 1 equiv. of lithium 1,3-diisopropylacetamidinate or lithium 1,3-di- tert-butylacetamidinate in diethyl ether at −78 °C afforded M(allyl)(iPrNC(Me)NiPr)(CO) 2(py) and M(allyl)(tBuNC(Me)NtBu)(CO) 2(py), respectively, in 68–78% yields. The new complexes were characterized by spectral and analytical methods and by X-ray crystal structure determinations. M(allyl)(iPrNC(Me)NiPr)(CO) 2(py) adopt pseudo-octahedral geometry about the metal centers, with the 1,3-diisopropylacetamidate ligand nitrogen atoms spanning one axial site and one equatorial site of the octahedron. By contrast, M(allyl)(tBuNC(Me)NtBu)(CO) 2(py) adopt pseudo-octahedral structures in which the two 1,3-di- tert-butylacetamidinate ligand nitrogen atoms span two equatorial coordination sites. Sublimation of M(allyl)(tBuNC(Me)NtBu)-(CO) 2(py) at 105 °C/0.03 Torr afforded ⩽7% yields of M(allyl)(tBuNC(Me)NtBu)(CO) 2, along with sublimed M(allyl)(tBuNC(Me)NtBu)(CO) 2(py). W(allyl)(tBuNC(Me)NtBu)(CO) 2 exists in the solid state as a 16-electron complex with distorted square pyramidal geometry. Many of the new complexes undergo dynamic ligand site exchange in solution, and these processes were probed by variable temperature 1H NMR spectroscopy. The volatilities and thermal stabilities were evaluated to determine the potential of the new complexes for use as precursors in thin film growth experiments.