The Five-Coordinate Hydrido−Dihydrogen Complex [OsH(η<SUP>2</SUP>-H<INF>2</INF>)(CO)(P<SUP>i</SUP>Pr<INF>3</INF>)<INF>2</INF>]BF<INF>4</INF> Acting as a Template for the Carbon−Carbon Coupling between Methyl Propiolate and 1,1-Diphenyl-2-propyn-1-ol

The five-coordinate hydrido−dihydrogen complex [OsH(η²-H<INF>2</INF>)(CO)(PⁱPr<INF>3</INF>)<INF>2</INF>]BF<INF>4</INF> (<BO>1</BO>) reacts with methyl propiolate in acetone to <ETIEBAR ID="om970713za10001">give [<TIEBAR NUM="om970713z00000">Os{C[C(</TIEBAR>O)OCH<INF>3</INF>]&dbd;CH<INF>2</INF>}{η¹-OC(CH<INF>3</INF>)<INF>2</INF>}(CO)(PⁱPr<INF>3</INF>)<INF>2</INF>]BF<INF>4</INF></ETIEBAR> (<BO>2</BO>). The acetone ligand of <BO>2</BO> can be easily displaced by methyl propiolate and 1,1-diphenyl-2-propyn-1-ol to <ETIEBAR ID="om970713za10002">afford [<TIEBAR NUM="om970713z00000">Os{C[C(</TIEBAR>O)OCH<INF>3</INF>]&dbd;CH<INF>2</INF>}(C&dbd;CHCO<INF>2</INF>CH<INF>3</INF>)(CO)(PⁱPr<INF>3</INF>)<INF>2</INF>]BF<INF>4</INF></ETIEBAR> (<BO>3</BO>) <ETIEBAR ID="om970713za10003">and [<TIEBAR NUM="om970713z00000">Os{C[C(</TIEBAR>O)OCH<INF>3</INF>]&dbd;CH<INF>2</INF>}(C&dbd;C&dbd;CPh<INF>2</INF>)(CO)(PⁱPr<INF>3</INF>)<INF>2</INF>]BF<INF>4</INF> (<BO>4</BO>),</ETIEBAR> respectively. The structure of <BO>4</BO> has been determined by X-ray diffraction. The geometry around the osmium atom can be rationalized as a distorted octahedron with the phosphine ligands occupying opposite positions. The remaining perpendicular plane is formed by the chelating alkenyl ligand, which acts with a bite angle of 62.8(2)°, the carbonyl group disposed trans to the oxygen atom. Complex <BO>4</BO> reacts with methyllithium to give the alkynyl derivative <ETIEBAR ID="om970713za10004">[<TIEBAR NUM="om970713z00000">Os{C[C(</TIEBAR>O)OCH<INF>3</INF>]&dbd;CH<INF>2</INF>}(C&tbd1;CCPh<INF>2</INF>CH<INF>3</INF>)(CO)(PⁱPr<INF>3</INF>)<INF>2</INF> (<BO>5</BO>),</ETIEBAR> which is unstable in methanol and quantitatively evolves <ETIEBAR ID="om970713za10005">into [<TIEBAR NUM="om970713z00000">Os{C[C(</TIEBAR>O)OCH<INF>3</INF>]&dbd;CH<INF>2</INF>}(C&tbd1;CCPh<INF>2</INF>OCH<INF>3</INF>)(CO)(PⁱPr<INF>3</INF>)<INF>2</INF> (<BO>6</BO>).</ETIEBAR> Complex <BO>6</BO> can be alternatively obtained from the reaction of <BO>4</BO> with NaOCH<INF>3</INF>. Complex <BO>4</BO> also reacts with NaCl to afford trans-chlorocarbonyl Os{C[C(O)OCH<INF>3</INF>]&dbd;CH<INF>2</INF>}Cl(C&dbd;C&dbd;CPh<INF>2</INF>)(CO)(PⁱPr<INF>3</INF>)<INF>2</INF> (<BO>7</BO>) and cis-chlorocarbonyl Os{C[C(O)OCH<INF>3</INF>]&dbd;CH<INF>2</INF>}Cl(C&dbd;C&dbd;CPh<INF>2</INF>)(CO)(PⁱPr<INF>3</INF>)<INF>2</INF> (<BO>8</BO>). At 60 °C, toluene solutions of <BO>7</BO> and <BO>8</BO> yield the <ETIEBAR ID="om970713za10006">allenyl derivative <TIEBAR NUM="om970713z00000">Os{C[C(&dbd;CH<INF>2</INF>)C(</TIEBAR>O)OCH<INF>3</INF>]&dbd;C&dbd;CPh<INF>2</INF>]Cl(CO)(PⁱPr<INF>3</INF>)<INF>2</INF> (<BO>9</BO>)</ETIEBAR> as a result from the migratory insertion of the allenylidene ligand into the Os−C(alkenyl) bond of <BO>7</BO> and <BO>8</BO>. The structure of <BO>9</BO> has been also determined by X-ray diffraction. The geometry around the osmium atom can be described as a distorted octahedron with the phosphine ligands occupying two relative trans positions. The ideal equatorial plane is formed by the chelate allenyl ligand which acts with a bite angle of 78.66(12)°, the carbonyl group disposed trans to the oxygen atom.