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Eight [CNN] pincer nickel NHC chlorides, [RCcarbeneNamidoR′2Namine–Ni–Cl] (R/R′2 = quinolinyl/nBu (3a), quinolinyl/Me (3b), quinolinyl/PhCH2 (3c), (CH2)4/nBu (5a), (CH2)4/iPr (5b), Me2/nBu (5c), Me2/iPr (5d), and Me2/PhCH2 (5e)), were prepared by the reactions of related asymmetric [CNN] NHC preligands with Ni(DME)Cl2via N–H bond activation. The molecular structures of complexes 3a, 3b and 5a were investigated using single crystal XRD. The catalytic experiments showed that the nickel complexes could catalyze the hydrosilylation of unsaturated compounds like aldehydes and ketones, and complex 3b was found to exhibit the best catalytic activity at 30 °C. Using NaBHEt3 as an additive, the catalytic activity of 3b was greatly improved. Furthermore, it was found that good to complete conversion of aldehydes could be achieved within 1.5 h at 30 °C after pre-reacting 3b and NaBHEt3 with silane for 0.5 h. The substrate ketones could be converted to alcohols in good yields by prolonging the reaction time to 2.5 h at 30 °C. It is worth mentioning that all eight [CNN] pincer nickel NHC chlorides are stable in air, and this is rare in nickel catalysts for hydrosilylation of aldehydes and ketones. Moreover, the substrate universality of the catalytic system is also very good, with good functional group tolerance. The molecular structures of complexes 3a, 3b and 5a were investigated using single crystal XRD and a possible reaction mechanism was proposed. [ABSTRACT FROM AUTHOR]

Three novel iron dinitrogen hydrides, [FeH(iPr-PSiMeP)(N2)(PMe3)] (1), [FeH(iPr-PSiPhP)(N2)(PMe3)] (2), and [FeH(iPr-PSiPh)(N2)(PMe3)] (3), supported by a silyl ligand are synthesized for the first time by changing the electronic effect and steric hindrance of the ligands through the reaction of ligands L1–L3 with Fe(PMe3)4 in a nitrogen atmosphere. The ligands containing an electron-donating group with large steric hindrance on the phosphorus atom are beneficial for the formation of dinitrogen complexes. A penta-coordinate iron hydride [FeH(iPr-PSiPh)(PMe3)2] (4) was formed through the reaction of ligand L3 with Fe(PMe3)4 in an argon atmosphere under the same conditions. The reactions between complexes 1–3 with an atmospheric pressure of dihydrogen gas resulted in Fe(II) dihydrides, [(iPr-PSiMe(μ-H)P)Fe(H)2(PMe3)] (5), [(iPr-PSiPh(μ-H)P)Fe(H)2(PMe3)] (6) and [(iPr-PSiPh(μ-H))Fe(H)2(PMe3)2] (7), with an η2-(Si–H) coordination. The isolation of dihydrides 5–7 demonstrates the ability of the dinitrogen complexes 1–3 to realize the activation of dihydrogen under ambient temperature and pressure. The molecular structures of complexes 1–7 were elucidated by single crystal X-ray diffraction analysis. The iron dinitrogen hydrides 1–3 are effective catalysts for the silylation of dinitrogen under ambient conditions and among them 3 is the best catalyst. [ABSTRACT FROM AUTHOR]

In this study, two [PCP] pincer silylene cobalt(I) complexes [((Ph2POCH2)2CH)Co(PMe3)(SiCl((NtBu)2CAr))] (Ar = Ph (2) and 4-MePh (3)) were synthesized through the substitution reaction of the [PCP] pincer cobalt(I) complex [((Ph2POCH2)2CH)Co(PMe3)2] (1) with silylene ligands: SiCl((NtBu)2CAr) (Ar = Ph (L1) and 4-MePh (L2)). The reaction of complex 2 with CO afforded the carbonyl silylene cobalt(I) complex [((Ph2POCH2)2CH)Co(CO)(SiCl((NtBu)2CPh))] (4), while complex 2 reacted with CH3I to give rise to cobalt(II) iodide [((Ph2POCH2)2CH)Co(I)(PMe3)] (6). With a catalyst loading of 2 mol%, complex 6 displayed efficient catalytic activity for hydrosilylation of alkenes by using Ph2SiH2 as the hydrogen source under mild conditions. The molecular structures of complexes 2, 3, 4 and 6 were determined by single crystal X-ray diffraction analysis. [ABSTRACT FROM AUTHOR]

Five [PSiP]-pincer iron hydrides 1–5, [(2-Ph2PC6H4)2HSiFe(H)(PMe3)2 (1), (2-Ph2PC6H4)2MeSiFe(H)(PMe3)2 (2), (2-Ph2PC6H4)2PhSiFe(H)(PMe3)2 (3), (2-(iPr)2PC6H4)2HSiFe(H)(PMe3) (4), and (2-(iPr)2PC6H4)2MeSiFe(H)(PMe3)2 (5)], were used as catalysts to study the effects of pyridine N-oxide and the electronic properties of [PSiP]-ligands on the catalytic hydrosilylation of carbonyl compounds. It was proved for the first time that this catalytic process could be promoted with pyridine N-oxide as the initiator at 30 °C because the addition of pyridine N-oxide is beneficial for the formation of an unsaturated hydrido iron complex, which is the key intermediate in the catalytic mechanism. Complex 4 as the best catalyst shows excellent catalytic performance. Among the five complexes, complex 3 was new and the molecular structure of complex 3 was determined by single crystal X-ray diffraction. A proposed mechanism was discussed. [ABSTRACT FROM AUTHOR]