Synthesis and some properties of 14 group element-containing alkylidene complexes of molybdenum and tungsten

Synthesis, structures and catalytic properties of germanium-containing tungsten alkylidene complex Me3Ge-CHW(NAr)(OR)2 and metallacycle [CH(GeMe3)CH(GeMe3)CH2]W(NAr)(OR)2

“…The C(1), C(9) atoms of tungstacyclobutane ring and OCMe 2 CF 3 ligand occupy equatorial positions whereas other alkoxide ligand and imido function are placed in apical sites. The spatial configuration of 2 is quite similar to that of the [CH(SiMe 3 The four-membered -W(1)-C(1)-C(5)-C(9)-metallacycle in 2 is bent. The dihedral angle between W(1)C(1)C9) and C(1)C(5)C(9) planes is 20.1°that is a significantly smaller than in 2a (29.9°) whereas the same metallacycle in 2b is absolutely flat.…”

“…However, it can be noted that (8) The alkylidene complex 1 and metallacycle 2 were found to reveal low catalytic activity in metathesis of neat 1-hexene. The rate constants (0.5 · 10 À5 L mol À1 s À1 and 1.8 · 10 À5 L mol À1 s À1 for 1 and 2, respectively) are one order of magnitude lesser than rate constant (1.73 · 10 À4 L mol À1 s À1 ) of the same reaction with similar germanium-containing molybdenum alkylidene complex Me 3 GeCH@Mo(NAr)(OCMe 2 CF 3 ) 2 as catalyst [3].…”

“…Thus, there are no significant differences in the geometric parameters of 1 and Me 3 E-CH@Mo(NAr)(OCMe 2 CF 3 ) 2 (E = Si, Ge) complexes. However, some difference between the complexes Me 3 E-CH@M(NAr)(OCMe 2 CF 3 ) 2 (M = Mo, W; E = Si, Ge) and Ph 3 E-CH@Mo(NAr)(OCMe 2 CF 3 ) 2 (E = Si, Ge) [3,4] should be noted. The bond angles M-C-E (M = Mo, W; E = Si, Ge) in the methyl alkylidene complexes (Mo-C-Si -138.5(1)°, Mo-C-Ge -137.57(10)°, W-C-Ge -137.7(2)°) are noticeably smaller than in the analogous phenyl alkylidene complexes (Mo-C-Si -144.8(2)°, Mo-C-Ge -144.1(1)°).…”

“…The kinetic experiments and determinations of rate constants were performed as described in the literature [3,11,12]. In a typical experiment to an ampoule containing 35.8 mg of catalyst and connected with gas burette 1.234 g (1.46 mL) of neat 1-hexene was added in argon atmosphere.…”

“…Much less known about similar molybdenum and tungsten compounds with heteroelement-containing substituents attached to carbene carbon [2]. We have recently found that catalytic activity of silicon-and germanium-containing alkylidene complexes of molybdenum R 3 E-CH@Mo-(NAr)(OCMe 2 CF 3 ) 2 (E = Si, Ge; R = Me, Ph) in metathesis of 1-hexene depended essentially on the nature of substituent bonded to carbene carbon atom [3].…”