mer, fac, and Bidentate Coordination of an Alkyl-POP Ligand in the Chemistry of Nonclassical Osmium Hydrides

Nonclassical and classical osmium polyhydrides containing the diphosphine 9,9-dimethyl-4,5-bis­(diisopropylphosphino)­xanthene (xant­(PiPr2)2), coordinated in κ3-mer, κ3-fac, and κ2-P,P fashions, have been isolated during the cyclic formation of H2 by means of the sequential addition of H+ and H– or H– and H+ to the classical trihydride OsH3Cl­{xant­(PiPr2)2} (1). This complex adds H+ to form the compressed dihydride dihydrogen complex [OsCl­(H···H)­(η2-H2)­{xant­(PiPr2)2}]+ (2). Under argon, cation 2 loses H2 and the resulting unsaturated fragment dimerizes to give [(Os­(H···H)­{xant­(PiPr2)2})2(μ-Cl)2]2+ (3). During the transformation the phosphine changes its coordination mode from mer to fac. The benzofuran counterpart of 1, OsH3Cl­{dbf­(PiPr2)2} (4; dbf­(PiPr2)2 = 4,6-bis­(diisopropylphosphino)­dibenzofuran), also adds H+ to afford the benzofuran counterpart of 2, [OsCl­(H···H)­(η2-H2)­{xant­(PiPr2)2}]+ (5), which in contrast to the latter is stable and does not dimerize. Acetonitrile breaks the chloride bridge of 3 to form the dihydrogen [OsCl­(η2-H2)­(CH3CN)­{xant­(PiPr2)2}]+ (6), regenerating the mer coordination of the diphosphine. The hydride ion also breaks the chloride bridge of 3. The addition of KH to 3 leads to 1, closing a cycle for the formation of H2. Complex 1 reacts with a second hydride ion to give OsH4{xant­(PiPr2)2} (7) as consequence of the displacement of the chloride. Similarly to the latter, the oxygen atom of the mer-coordinated diphosphine of 7 has a tendency to be displaced by the hydride ion. Thus, the addition of KH to 7 yields [OsH5{xant­(PiPr2)2}]− (8), containing a κ2-P,P-diphosphine. Complex 8 is easily protonated to afford OsH6{xant­(PiPr2)2} (9), which releases H2 to regenerate 7, closing a second cycle for the formation of molecular hydrogen.

以双膦配体（diphosphine）9,9-二甲基-4,5-双(二异丙基膦基)呫吨（xant(PiPr₂)₂，英文全称：9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene）配位的经典与非经典锇多氢化物（osmium polyhydrides），在向经典三氢氯化锇OsH₃Cl{xant(PiPr₂)₂}（1）依次添加H⁺与H⁻或H⁻与H⁺以实现氢气循环生成的过程中被分离得到。配合物1可与H⁺发生加成反应，得到压缩型二氢-η²-双氢合锇阳离子[OsCl(H···H)(η²-H₂){xant(PiPr₂)₂]⁺（2）。在氩气保护下，阳离子2脱去H₂，所得不饱和金属片段发生二聚，生成双核μ-氯桥联配合物[(Os(H···H){xant(PiPr₂)₂)₂(μ-Cl)₂]²⁺（3），该过程中膦配体的配位模式由κ³-矫式（κ³-mer）转变为κ³-面式（κ³-fac）。配合物1的苯并呋喃类似物OsH₃Cl{dbf(PiPr₂)₂}（4；dbf(PiPr₂)₂ = 4,6-双(二异丙基膦基)二苯并呋喃（4,6-bis(diisopropylphosphino)dibenzofuran））也可与H⁺加成，得到配合物2的苯并呋喃类似物[OsCl(H···H)(η²-H₂){xant(PiPr₂)₂]⁺（5），但与配合物2不同，配合物5性质稳定，不会发生二聚。乙腈可断裂配合物3中的氯桥，生成η²-双氢合锇阳离子[OsCl(η²-H₂)(CH₃CN){xant(PiPr₂)₂]⁺（6），同时恢复双膦配体的κ³-矫式配位模式。氢负离子同样可断裂配合物3中的氯桥。向配合物3中加入KH可得到配合物1，由此完成第一个氢气生成循环。配合物1可与第二个氢负离子反应，因氯离子被取代，生成OsH₄{xant(PiPr₂)₂}（7）。与配合物7类似，其κ³-矫式配位双膦配体的氧原子也存在被氢负离子取代的趋势。向配合物7中加入KH可得到[OsH₅{xant(PiPr₂)₂]⁻（8），该配合物中的双膦配体以κ²-P,P配位模式。配合物8可被轻松质子化，得到OsH₆{xant(PiPr₂)₂}（9），后者可脱去H₂并再生配合物7，由此完成第二个氢气生成循环。