Zerovalent Nickel Compounds Supported by 1,2-Bis(diphenylphosphino)benzene: Synthesis, Structures, and Catalytic Properties

Abstract

Zerovalent nickel compounds which feature 1,2-bis(diphenylphosphino)benzene (dppbz) were obtained via the reactivity of dppbz towards Ni(PMe), which affords sequentially (dppbz)Ni(PMe) and Ni(dppbz). Furthermore, the carbonyl derivatives (dppbz)Ni(PMe)(CO) and (dppbz)Ni(CO) may be obtained via the reaction of CO with (dppbz)Ni(PMe). Other methods for the synthesis of these carbonyl compounds include (i) the formation of (dppbz)Ni(CO) by the reaction of Ni(PPh)(CO) with dppbz and (ii) the formation of (dppbz)Ni(PMe)(CO) by the reaction of (dppbz)Ni(CO) with PMe. Comparison of the ν(CO) IR spectroscopic data for (dppbz)Ni(CO) with other (diphosphine)Ni(CO) compounds provides a means to evaluate the electronic nature of dppbz. Specifically, comparison with (dppe)Ni(CO) indicates that the o-phenylene linker creates a slightly less electron donating ligand than does an ethylene linker. The steric impact of the dppbz ligand in relation to other diphosphine ligands has also been evaluated in terms of its buried volume (%V) and steric maps. The nickel center of (dppbz)Ni(PMe) may be protonated by formic acid at room temperature to afford [(dppbz)Ni(PMe)H], but at elevated temperatures, effects catalytic release of H from formic acid. Analogous studies with Ni(dppbz) and Ni(PMe) indicate that the ability to protonate the nickel centers in these compounds increases in the sequence Ni(dppbz) < (dppbz)Ni(PMe) < Ni(PMe); correspondingly, the pK values of the protonated derivatives increase in the sequence [Ni(dppbz)H] < [(dppbz)Ni(PMe)H] < [Ni(PMe)H]. (dppbz)Ni(PMe) and Ni(PMe) also serve as catalysts for the formation of alkoxysilanes by (i) hydrosilylation of PhCHO by PhSiH and PhSiH and (ii) dehydrocoupling of PhCHOH with PhSiH and PhSiH.

Photoactivated silicon–oxygen and silicon–nitrogen heterodehydrocoupling with a commercially available iron compound

“…29,30 Analogously, Parkin and co-workers have reported Si-O heterodehydrocoupling between PhSiH3 and BnOH via nickel-catalysts, however, to a mixture of PhSiH(OBn)2 and PhSi(OBn)3 after 24 h at 80°C. 31 Reactions between i PrOH and PhSiH3 at similar alcohol/silane ratio proceeded to incomplete conversion from PhSiH3 after 24 h, which prompted an increase in the alcohol/silane ratio. Reaction of a 5:1 mixture of i PrOH and PhSiH3 completely converted from PhSiH3 by 24 h to PhSi(O i Pr)3 (Table 1, Entry 3).…”

“…Ph2Si(OBn)2 in significantly shorter reactions times, however, elevated heating appears to be a necessary factor in these reactions. 31,36,37 Interestingly, reacting 5 equiv of i PrOH with Ph2SiH2 exclusively yielded Ph2SiH(O i Pr) 25 in quantitative conversion with no evidence of the fully substituted product Ph2Si(O i Pr)2 (Table 1, Entry 9). 30 Reaction of n PrOH and PhMe2SiH in a 5:1 ratio afforded a new product, tentatively assigned to PhMe2Si(O n Pr) based on analogy to PhMe2Si(OBn) and PhMe2Si(O i Pr), in 93% conversion as a resonance at δ 6.67 in the 29 Si{ 1 H} NMR spectrum (Table 1, Entry 10).…”

N-Heterocyclic Carbene Complexes of Nickel, Palladium, and Iridium Derived from Nitron: Synthesis, Structures, and Catalytic Properties

“…We are currently interested in developing catalytic applications of metal complexes with respect to transformations that involve C–O bonds. As an illustration, we have previously described catalysts for the (i) decarboxylation of formic acid to release H 2 , a reaction that is of interest regarding the use of formic acid as a medium for storing hydrogen with respect to energy applications, , and (ii) hydrosilylation of carbonyl compounds, including the conversion of CO 2 to silyl formates and bis­(silyl)­acetals. − Since NHC ligands have found widespread use in catalysis, we sought to develop catalytic applicatons of Nitron NHC metal complexes. Therefore, it is of note that (Nitron NHC )­Ir­(CO) 2 Cl provides a catalyst for the dehydrogenation of formic acid (Scheme ) at 80 °C. − …”

Photoactivated Silicon–Oxygen and Silicon–Nitrogen Heterodehydrocoupling with a Commercially Available Iron Compound

“…Ph2Si(OBn)2 in significantly shorter reactions times, however, elevated heating appears to be a necessary factor in these reactions. 31,36,37 Interestingly, reacting 5 equiv of i PrOH with Ph2SiH2 exclusively yielded Ph2SiH(O i Pr) 25 in quantitative conversion with no evidence of the fully substituted product Ph2Si(O i Pr)2 ( 39 Finally, attempts at coupling alcohols to the tertiary alkyl silane Et3SiH produced no change in 1 H NMR spectroscopy after 24 h.…”