Reactions of manganese silyl dihydride complexes with CO2

Under mild conditions (room temperature, 1.1 atm. of CO2), the silyl dihydride complexes [(dmpe)2MnH2(SiHR2)] {R = Ph (1 Ph2 ); Et (1 Et2 )} reacted rapidly and quantitatively with carbon dioxide to afford [(dmpe)2MnH2{Si(κ 1-O2CH)R2)}] {R = Ph (2 Ph2 ); Et (2 Et2 )}; the products of apparent CO2 insertion into the terminal SiH bond. In addition, room temperature reactions of [(dmpe)2MnH2(SiH2R)] {R = Ph (1 Ph ); n Bu (1 Bu )} with CO2 (1.1 atm.) yielded [(dmpe)2MnH2{Si(κ 1-O2CH)2R)}] {R = Ph (3 Ph ); n Bu (3 Bu )} containing two formate substituents on silicon. The latter reactions proceeded in a stepwise fashion, rapidly forming [(dmpe)2MnH2{SiH(κ 1-O2CH)R}] {R = Ph (4 Ph ); n Bu (4 Bu )} intermediates, which then slowly converted into 3 Ph and 3 Bu . During the syntheses of 3 Ph and 3 Bu , significant amounts of H2 and previously reported [(dmpe)2Mn(CO)(κ 1-O2CH)] (5) were also formed. The reaction of [(dmpe)2MnD2(SiH2 n Bu)] ( d 2 -1 Bu ) with CO2 was carried out, yielding d 2 -3 Bu as the major reaction product, predominantly (>95%) as [(dmpe)2MnD2{Si(κ 1-O2CH)2 n Bu}] featuring two deuteride ligands. DFT calculations to probe the relative energies of silicate [(dmpe)2Mn(η 3-H2SiR3)], trans-hydrosilane/hydride (trans-[(dmpe)2MnH(H–SiR3)]), trans-dihydrogen/silyl (trans-[(dmpe)2Mn(H2)(SiR3)]), and lateral-dihydrogen/silyl (cis-[(dmpe)2Mn(H2)(SiR3)]) isomers of 2 Ph2 , 3 Ph , and 4 Ph are also reported; the lowest energy structures of 2 Ph2 and 3 Ph are those of the silicate isomers, consistent with the NMR spectra obtained for 2 R2 and 3 R . Also, compound 2 Ph2 was isolated, and crystallized as the silicate isomer; the solid state structure of 2 Ph2 is qualitatively analogous to that of 1 Ph2 , but the MnSi bond in 2 Ph2 is significantly shorter {2.2876(7)Å vs 2.3176(3) Å}.