Net [2 + 2] cycloaddition reactions of the oxo complexes Cp2M:O (M = Mo, W) with electrophilic organic and organometallic substrates. Formation of bimetallic .mu.2-.eta.3-CO2 complexes

Catalytic Degenerate and Nondegenerate Oxygen Atom Transfers Employing N2O and CO2 and a MII/MIV Cycle Mediated by Group 6 MIV Terminal Oxo Complexes

“…[18,19] As shown in Scheme 2, addition of a slight excess of tBuNC to a toluene solution of 7 and 8, followed by removal of toluene in vacuo and crystallization from pentane at À30 8C for 18 h, provided modest to excellent yields of the corresponding diamagnetic, crystalline complexes, [Cp*M{h 2 -OCNtBu)}(CNtBu){N(iPr)C(Me)N(iPr)}] where M = Mo (9) and W (10). [9] Importantly, single-crystal X-ray analyses of 9 and 10 served to establish a k 2 -(O,C) ligation of the tBuNCO group, which, to the best of our knowledge, is the first time that this coordination mode for a metal-complexed isocyanate has been unequivocally established.…”

“…[5,23] Indeed, literature precedent would appear to argue against the probability of success in achieving such a goal for the Group 6 metals. More specifically, Mayer and co-workers [18] Thus, the key to establishing the catalytically competent OAT cycle for the oxidation of isocyanides to isocyanates that is presented in Scheme 4 was the discovery that, in solution, both 7 and 8 are unreactive towards an excess of tBuNCO; presumably due to a decreased nucleophilicity of the oxo group that is associated with a higher MÀO bond order (see above). More specifically, starting with a 5:1 ratio of tBuNC to 11 (prepared in situ from 1) in [D 6 ]benzene solution at 25 8C under an atmosphere of N 2 O (10 psi) within a sealed NMR tube, 1 H NMR spectroscopy clearly showed the clean and steady production of multiple equivalents of tBuNCO.…”

Catalytic Degenerate and Nondegenerate Oxygen Atom Transfers Employing N2O and CO2 and a MII/MIV Cycle Mediated by Group 6 MIV Terminal Oxo Complexes

“…[17] This bond order formalization for 7 and 8 further implies a lower nucleophilicity for the terminal oxo group, as compared to that experimentally determined for [(MeCp) 2 M(O)] and related metallocene terminal oxo complexes, such as [Cp 2 M(O)] (Cp = h 5 -C 5 H 5 ) and [Cp* 2 M(O)]. [18,19] As shown in Scheme 2, addition of a slight excess of tBuNC to a toluene solution of 7 and 8, followed by removal of toluene in vacuo and crystallization from pentane at À30 8C for 18 h, provided modest to excellent yields of the corresponding diamagnetic, crystalline complexes, [Cp*M{h 2 -OCNtBu)}(CNtBu){N(iPr)C(Me)N(iPr)}] where M = Mo (9) and W (10). [9] Importantly, single-crystal X-ray analyses of 9 and 10 served to establish a k 2 -(O,C) ligation of the tBuNCO group, which, to the best of our knowledge, is the first time that this coordination mode for a metal-complexed isocyanate has been unequivocally established.…”

“…Furthermore, it is well known that the nucleophilic character of the oxo moiety in the Group 6 metallocene derivatives, [Cp 2 M(O)] (M = Mo and W), facilitates a variety of [2+2] cycloadditions with isocyanates and other electrophiles. [18] Thus, the key to establishing the catalytically competent OAT cycle for the oxidation of isocyanides to isocyanates that is presented in Scheme 4 was the discovery that, in solution, both 7 and 8 are unreactive towards an excess of tBuNCO; presumably due to a decreased nucleophilicity of the oxo group that is associated with a higher MÀO bond order (see above). More specifically, starting with a 5:1 ratio of tBuNC to 11 (prepared in situ from 1) in [D 6 ]benzene solution at 25 8C under an atmosphere of N 2 O (10 psi) within a sealed NMR tube, 1 H NMR spectroscopy clearly showed the clean and steady production of multiple equivalents of tBuNCO.…”

Quantum chemical studies on a series of transition metal carbon dioxide complexes: Metal–carbon bonding and electronic structures

“…Complexes in class I have two equal M-O bonds. The first reported complex in class I is the rhenium/tungsten cationic complex 6 [58,59]. X-ray studies show that the Rh-C bond is short at 2.04 Å , and the two C-O bond distances are 1.34 and 1.32 Å .…”