TY - JOUR
T1 - Partnering a Three-Coordinate Gallium Cation with a Hydroborate Counter-Ion for the Catalytic Hydrosilylation of CO2
AU - Caise, Alexa
AU - Hicks, Jamie
AU - Ángeles Fuentes, M.
AU - Goicoechea, Jose M.
AU - Aldridge, Simon
N1 - Publisher Copyright:
© 2020 Wiley-VCH GmbH
PY - 2021/1/26
Y1 - 2021/1/26
N2 - A novel β-diketiminate stabilized gallium hydride, (DippL)Ga(Ad)H (where (DippL)={HC(MeCDippN)2}, Dipp=2,6-diisopropylphenyl and Ad=1-adamantyl), has been synthesized and shown to undergo insertion of carbon dioxide into the Ga−H bond under mild conditions. In this case, treatment of the resulting κ1-formate complex with triethylsilane does not lead to regeneration of the hydride precursor. However, when combined with B(C6F5)3, (DippL)Ga(Ad)H catalyses the reductive hydrosilylation of CO2. Under stoichiometric conditions, the addition of one equivalent of B(C6F5)3 to (DippL)Ga(Ad)H leads to the formation of a 3-coordinate cationic gallane complex, partnered with a hydroborate anion, [(DippL)Ga(Ad)][HB(C6F5)3]. This complex rapidly hydrometallates carbon dioxide and catalyses the selective reduction of CO2 to the formaldehyde oxidation level at 60 °C in the presence of Et3SiH (yielding H2C(OSiEt3)2). When catalysis is undertaken in the presence of excess B(C6F5)3, appreciable enhancement of activity is observed, with a corresponding reduction in selectivity: the product distribution includes H2C(OSiEt3)2, CH4 and O(SiEt3)2. While this system represents proof-of-concept in CO2 hydrosilylation by a gallium hydride system, the TOF values obtained are relatively modest (max. 10 h−1). This is attributed to the strength of binding of the formatoborate anion to the gallium centre in the catalytic intermediate (DippL)Ga(Ad){OC(H)OB(C6F5)3}, and the correspondingly slow rate of the turnover-limiting hydrosilylation step. In turn, this strength of binding can be related to the relatively high Lewis acidity measured for the [(DippL)Ga(Ad)]+ cation (AN=69.8).
AB - A novel β-diketiminate stabilized gallium hydride, (DippL)Ga(Ad)H (where (DippL)={HC(MeCDippN)2}, Dipp=2,6-diisopropylphenyl and Ad=1-adamantyl), has been synthesized and shown to undergo insertion of carbon dioxide into the Ga−H bond under mild conditions. In this case, treatment of the resulting κ1-formate complex with triethylsilane does not lead to regeneration of the hydride precursor. However, when combined with B(C6F5)3, (DippL)Ga(Ad)H catalyses the reductive hydrosilylation of CO2. Under stoichiometric conditions, the addition of one equivalent of B(C6F5)3 to (DippL)Ga(Ad)H leads to the formation of a 3-coordinate cationic gallane complex, partnered with a hydroborate anion, [(DippL)Ga(Ad)][HB(C6F5)3]. This complex rapidly hydrometallates carbon dioxide and catalyses the selective reduction of CO2 to the formaldehyde oxidation level at 60 °C in the presence of Et3SiH (yielding H2C(OSiEt3)2). When catalysis is undertaken in the presence of excess B(C6F5)3, appreciable enhancement of activity is observed, with a corresponding reduction in selectivity: the product distribution includes H2C(OSiEt3)2, CH4 and O(SiEt3)2. While this system represents proof-of-concept in CO2 hydrosilylation by a gallium hydride system, the TOF values obtained are relatively modest (max. 10 h−1). This is attributed to the strength of binding of the formatoborate anion to the gallium centre in the catalytic intermediate (DippL)Ga(Ad){OC(H)OB(C6F5)3}, and the correspondingly slow rate of the turnover-limiting hydrosilylation step. In turn, this strength of binding can be related to the relatively high Lewis acidity measured for the [(DippL)Ga(Ad)]+ cation (AN=69.8).
KW - beta-diketiminate
KW - carbon dioxide
KW - gallium
KW - hydride
KW - hydrosilylation
KW - reduction
UR - http://www.scopus.com/inward/record.url?scp=85098143713&partnerID=8YFLogxK
U2 - 10.1002/chem.202004408
DO - 10.1002/chem.202004408
M3 - Article
SN - 0947-6539
VL - 27
SP - 2138
EP - 2148
JO - Chemistry - A European Journal
JF - Chemistry - A European Journal
IS - 6
ER -