Synthesis and Reactivity of Silyl Iron, Cobalt, and Nickel Complexes Bearing a [PSiP]-Pincer Ligand via Si–H Bond Activation

The synthesis and characterization of a series of Ni, Co, and Fe complexes bearing a tridentate bis­(phosphino)­silyl ligand (κ³-(2-Ph₂PC₆H₄)₂SiMeH, [PSiP]-H, <b>1</b>) are reported. <b>1</b> reacted with Ni­(PMe₃)₄ to afford the mononuclear nickel(0) complex [η²(Si–H)-PSiP]­Ni­(PMe₃) (<b>2</b>). The halogeno nickel complexes [PSiP]­Ni­(X)­(PMe₃) (X = Cl (<b>3</b>)<b>,</b> Br (<b>4</b>), I (<b>5</b>)) were synthesized in the reactions of <b>2</b> with Me₃SiCl or MeHSiCl₂, EtBr, and MeI. Complex <b>2</b> underwent ligand substitution of PMe₃ by CO to give [η²(Si–H)-PSiP]­Ni­(CO) (<b>6</b>). Complex <b>3</b> reacted with NaOMe to deliver [PSiP]­Ni­(OMe)­(PMe₃) (<b>7</b>) through anionic ligand substitution, while the neutral ligand replacement of PMe₃ by CO in <b>3</b> afforded the rare hexacoordinate 20-electron nickel­(II) complex [PSiP]­Ni­(Cl)­(CO)₂ (<b>8</b>). Unexpectedly, reaction of <b>1</b> with NiMe₂(PMe₃)₃ produced the tetracoordinate nickel(0) complex [Me₂PSiP]₂Ni (<b>9</b>). The complex [Me₂PSiP]­Ni­(CO)₂ (<b>10</b>) was acquired from <b>9</b> after the substitution of one [PSiP] ligand by two carbonyl ligands. <b>1</b> reacted with Co­(PMe₃)₄ or CoCl­(PMe₃)₃ to afford the hydrido cobalt­(II) complex [PSiP]­CoH­(PMe₃) (<b>11</b>) or hydrido cobalt­(III) complex [PSiP]­Co­(H)­(Cl)­(PMe₃) (<b>13</b>). Complex <b>12</b>, [PSiP]­Co­(H)­(I)­(PMe₃), could be obtained from the reaction of MeI with <b>11</b> or <b>13</b>. Treatment of <b>13</b> with 1 equiv of MeLi or <i>n</i>-BuMgBr in THF resulted in the clean formation of cobalt­(I) complex [PSiP]­Co­(PMe₃)₂ (<b>14</b>) via reductive elimination. The simple anhydrous inorganic salt NiCl₂ or CoCl₂ could also react with <b>1</b> in the presence of PMe₃ to form the corresponding silyl complexes <b>3</b> and [PSiP]­Co­(Cl)­(PMe₃) (<b>15</b>) via Si–H bond cleavage. <b>1</b> reacted with Fe­(PMe₃)₄ to form the hexacoordinate octahedral hydrido iron­(II) complex [PSiP]­Fe­(H)­(PMe₃)₂ (<b>16</b>). The molecular structures of complexes <b>2</b>–<b>5</b>,<b> 10</b>,<b> 12</b>,<b> 13</b>,<b> 15</b>, and <b>16</b> were determined by X-ray single crystal diffraction. <b>16</b> has excellent catalytic reactivity for the reduction of aldehydes and ketones