Relevance to Synthetic Polynuclear Chemistry of Novel μ3-Coordination Modes for the Anions Ph2PCHCOOC2H2- and Mo(CO)3Cp-. Synthesis and X-ray structure of Pd(8-mq)Br(Ph2PCH2COOC2H5), (3(μ3-Ph2PCHCOOC2H5)(μ3-OH))PF6, and (3<μ

Article abstract of DOI:10.1021/ja00314a026

The analogous role structurally played by the μ₂-organophosphorus 2PCHC(O)OC₂H₅> and the μ₂-organometallic 3Cp> bridges is illustrated by the molecular structure of the complexes (1) and <(8-mq)Pd>₂(μ-Cl)(μ-Mo(CO)₃Cp) (3) (8-mq-H=8-methylquinoline).These bridges act in these molecules as three-electron donors.The analogy is further demonstrated by the reaction of 1 and 3 with Ag⁺, leading respectively to the tri- and tetrametallic complexes (₃(μ₃-Ph₂PCHCOOC₂H₅)(μ₃-OH))PF₆ (2) and (₃(μ₃-Mo(CO)₃Cp)(μ₃-Cl))BF₄ (5a).The structure of both products was established by single-crystal X-ray analysis.Crystals of 2 belong to the space group P2₁/n, with a=23.573(9) Angstroem, b=15.789(5) Angstroem, c=12.381(4) Angstroem, β=100.21(2) deg, V=4535 Angstroem³, and Z=4.The structure has been refined to R=0.073 and R_W=0.087.The molecule consists of three Pd(8-mq) fragments held together by a μ₃-OH group and the Y ligand μ₃-bonded through the phosphorus, the α-carbon, and oxygen (C=O) atoms, respectively, to each of the palladium atoms.Complex 5a crystallizes in the space group C2/c, with a=23.877(9) Angstroem, b=17.315(6) Angstroem, c=19.142(7) Angstroem, β=111.80(2) deg, V=7348 Angstroem³, and Z=8.The refinement of the structure has led to R=0.047 and R_W=0.063.The molecular structure shows three separated Pd centers bridged by a μ₃-Cl atom and a μ₃-Mo(CO)₃Cp moiety.The four metal atoms, the three carbon atoms of the carbonyls, and the bridging chloride define a distorted cubane structure for the inorganic core of 5a.The unique bonding mode of Mo(CO)₃Cp involving the metal and all three carbonyls provides the first example where such a unit is coordinated to three metal centers.Complexes 2 and 5a are envisaged as resulting from the addition of the unsaturated fragment to 1 and 3, respectively.In the first case, this is made possible by additional coordination through the ester function, and in the second case, by increased coordination from μ₂ to μ₃ of the bridging Cl and Mo(CO)₃Cp groups.This concept was verified by the rational quantitative synthesis of 5a resulting from the addition of 1 equiv of 3CN)₂>⁺ (4) to 3.The analogy between the μ₃ organic fragment in 2 and μ₃-Mo(CO)₃Cp in 5a allows their description as five-electron donors.The geometry of the cyclometalated 8-mq units of 2 and 5a is discussed and compared to that of Pd(8-mq)Br(Ph₂PCH₂COOC₂H₅) (6).The molecular structure of the latter complex was established by X-ray diffraction: C2/c with a=18.691(3) Angstroem, b=14.940(1) Angstroem, c=17.722(1) Angstroem, β=97.27(2) deg, V=4909 Angstroem³, and Z=8.