Multiply Bonded Dimetal Complexes Containing Bis(diphenylphosphino)methane Bridges: Complexes Possessing Rhenium-Rhenium Double Bonds and a Tungsten-Tungsten Single Bond

Article abstract of DOI:10.1021/ja00322a024

The quadruply bonded dirhenium(III)complex (n-Bu4N)2Re2Cl8 reacts with bis(diphenylphosphino)methane (dppm) in dichloromethane to produce the complex Re2Cl6(dppm)2 (I).The structurally analogous complex Re2Cl6(Ph2Ppy)2 (II) has been isolated from the reaction between (n-Bu4N)2Re2Cl8 and Ph2Ppy in acetonitrile.When primary alcohols (ROH) are used as solvents, (n-Bu4N)2Re2Cl8 reacts with dppm to form the alkoxide complexes Re2Cl5(OR)(dppm)2 (R=CH3, IIIa; R=CH2CH3, IIIb; R=CH2CH2CH3, IIIc).When the quadruply bonded complex Re2Cl6(P-n-Bu3)2 is used in place of (n-Bu4N)2Re2Cl8, then the reaction with dppm in methanol yields Re2Cl4(dppm)2, while with diethyl ether as the solvent Re2Cl5(dppm)2 is formed.All of the preceding complexes exhibit well-defined electrochemical properties.Electrolysis of dichloromethane solutions of Re2Cl4(dppm)2, containing an excess of Cl^-, at a potential of +0.60 V vs.SCE first generates Re2Cl5(dppm)2, which is in turn converted to Re2Cl6(dppm)2.This potential (+0.60 V) is sufficient to oxidize Re2Cl4(dppm)2 to its monocation and, following the conversion of the letter to Re2Cl5(dppm)2 upon its reaction with Cl^-, also to convert Re2Cl5(dppm)2 to ⁺, which in turn reacts with Cl^-.The complexes I and IIIb have been structurally characterized by X-ray chrystallography and shown to have structures which conform to the notion that these molecules possess rhenium-rhenium double bonds as predicted by Hoffmann.Using the bidentate ligand bis(diphenylphosphino)amine(dppa), we have prepared the complexes Re2Cl6(dppa)2, Re2Cl4(dppa)2, and Re2Cl4(PMePh2)2(dppa) and the ⁺ cation (either as the Cl^- or PF6^- salt).The spectroscopic and electrochemical properties of the dirhenium species show a very close similarity to those of their dppm analogues, implying a close similarity of structure.To further explore the influence of replacing a terminal Cl ligand by OR on the M-M bond length we have also examined the structure of W2(μ-O-i-Pr)2(O-i-Pr)6Cl2 and compare it with that of W2(μ-OEt)2(OEt)4Cl4.Again the OR for Cl replacement causes a lengthening of the M-M bond.Re2Cl6(dppm)2 crystallizes in the monoclinic space group C2/c with cell parameters a=23.083(3) Angstroem, b=10.866(3) Angstroem, c=23.253(5) Angstroem, β=124.25(2) deg, Z=4.The structure of Re2Cl5(OC2H5)(dppm)2 was solved and refined in the orthorhombic space group Pn2₁a with cell parameters a=24.099(8) Angstroem, b=18.225(4) Angstroem, c=12.565(4) Angstroem,.W2(O-i-Pr)8Cl2 forms monoclinic crystals in space group C2/m with a=17.706(4) Angstoem, b=12.034(2) Angstroem, c=9.727(2) Angstroem, β=123.74(2) deg, Z=2.