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Abstract: The terminal zinc hydride complex [Tntm]ZnH (2; Tntm=tris(6‐tert‐butyl‐3‐thiopyridazinyl)methanide) is an efficient hydrosilylation catalyst of CO2 at room temperature without the need of Lewis acidic additives. The inherent electrophilicity of the system leads to selective formation of the monosilylated product (MeO)3SiO2CH (at room temperature with a TOF of 22.2 h−1 and at 45 °C with a TOF of 66.7 h−1). In absence of silanes, the intermediate formate complex [Tntm]Zn(O2CH) (3) is quantitatively formed within 5 min. All complexes were fully characterized by 1H and 13C NMR spectroscopy and single‐crystal X‐ray diffraction analyses. Density functional theory (DFT) calculations reveal a high positive charge on zinc and the increased preference of the ligand to adopt a κ3‐coordination mode. [ABSTRACT FROM AUTHOR]

Tris(2-pyridylthio)methyl zinc hydride, [κ3-Tptm]ZnH, is an effective catalyst for multiple insertions of carbonyl groups into the Si-H bonds of PhxSiH4-x (x = 1, 2). Specifically, [κ3-Tptm]ZnH catalyzes the insertion of a variety of aldehydes and ketones into the Si-H bonds of PhSiH3 and Ph2SiH2 to afford PhSi[OCH(R)R']3 and Ph2Si[OCH(R)R']2, respectively. The mechanism for hydrosilylation is proposed to involve insertion of the carbonyl group into the Zn-H bond to afford an alkoxy species, followed by metathesis with the silane to release the alkoxysilane and regenerate the zinc hydride catalyst. Multiple insertion of prochiral ketones results in the formation of diastereomeric mixtures of alkoxysilanes that can be identified by NMR spectroscopy. [ABSTRACT FROM AUTHOR]

Tris(2-pyridylthio)methylzinc hydride, [κ3-Tptm]ZnH,is an effective catalyst for multiple insertions of carbonyl groupsinto the Si–H bonds of PhxSiH4–x(x= 1, 2). Specifically,[κ3-Tptm]ZnH catalyzes the insertion of a varietyof aldehydes and ketones into the Si–H bonds of PhSiH3and Ph2SiH2to afford PhSi[OCH(R)R′]3and Ph2Si[OCH(R)R′]2, respectively.The mechanism for hydrosilylation is proposed to involve insertionof the carbonyl group into the Zn–H bond to afford an alkoxyspecies, followed by metathesis with the silane to release the alkoxysilaneand regenerate the zinc hydride catalyst. Multiple insertion of prochiralketones results in the formation of diastereomeric mixtures of alkoxysilanesthat can be identified by NMR spectroscopy. [ABSTRACT FROM AUTHOR]

The trinuclear cationic zinc hydride cluster [(IMes)3Zn3H4(THF)](BPh4)2 ( 1) was obtained either by protonation of the neutral zinc dihydride [(IMes)ZnH2]2 with a Brønsted acid or by addition of the putative zinc dication [(IMes)Zn(THF)]2+. A triply bridged thiophenolato complex 2 was formed upon oxidation of 1 with PhSSPh. Protonolysis of 1 by methanol or water gave the corresponding trinuclear dicationic derivatives. At ambient temperature, 1 catalyzed the hydrosilylation of aldehydes, ketones, and nitriles. Carbon dioxide was also hydrosilylated under forcing conditions when using (EtO)3SiH, giving silylformate as the main product. [ABSTRACT FROM AUTHOR]

We present isolable examples of formal zinc hydride cations supported by N-heterocyclic carbene (NHC) donors, and investigate the dual electrophilic and nucleophilic (hydridic) character of the encapsulated [ZnH]+ units by computational methods and preliminary hydrosilylation catalysis. [ABSTRACT FROM AUTHOR]

Generation of H2 from methanol/water and hydrosilylation of CO2 catalyzed by [tris(2-pyridylthio)methyl]zinc hydride [κ³-Tptm]ZnH 1 were investigated with DFT and MP2 methods. The hydrosilylation of CO2 occurs via the CO2 insertion into the Zn-H bond of 1 followed by the metathesis of a Zn-(η¹-OCOH) bond with hydrosilane to yield silyl formate and regenerate 1. The CO2 insertion easily occurs, but the metathesis is difficult because of the formation of a very stable Zn-(η²-O2CH) species before the metathesis. The ΔGº‡ value of the metathesis with triethoxysilane is much smaller than that with phenylsilane because electronegative methoxy groups stabilize the transition state bearing hypervalent Si center, which is consistent with the experimental result that triethoxysilane is used in the hydrosilylation of C O2. It is theoretically predicted here that hydrosilane with two electronegative OEt groups or one to three F groups can be applied to this reaction. In the generation of H2 from methanol/water by 1, the first step is the metathesis of 1 with the O-H bond of methanol/water to produce [κ³-Tptm]Zn(OMe)/[k³-Tptm]Zn(OH) and dihydrogen molecule. The next step is the metathesis of the Zn-OMe/ Zn-OH bond with hydrosilane to yield silyl ether and regenerate 1. The first metathesis is rate-determining but the second one occurs with very small activation energy, indicating that various hydrosilanes can be applied to this reaction. [ABSTRACT FROM AUTHOR]

[Tris(2-pyridylthio)methyl]zinc hydride, [κ3-Tptm]ZnH, is a multifunctional catalyst that is capable of achieving (i) rapid release of hydrogen by protolytic cleavage of silanes with either water or methanol and (ii) hydrosilylation of aldehydes, ketones, and carbon dioxide. For example, [κ3-Tptm]ZnH catalyzes the release of 3 equivalents of H2 by methanolysis of phenylsilane, with a turnover number of 105 and a turnover frequency surpassing 106 h-1 for the first 2 equivalents. Furthermore, [κ3-Tptm]ZnH also catalyzes the formation of triethoxysilyl formate by hydrosilylation of carbon dioxide with triethoxysilane. Triethoxysilyl formate may be converted into ethyl formate and N,N-dimethylformamide, thereby providing a means for utilizing carbon dioxide as a C1 feedstock for the synthesis of useful chemicals. [ABSTRACT FROM AUTHOR]