Synthesis, Characterization, and Reactions of Functionalized Nickel–Iron Dithiolates Related to the Active Site of [Nife]-Hydrogenases

A series of new models for the active site of [NiFe]-H(2)ases have been prepared by simple and convenient methods. Thus, treatment of diphosphine-chelated Ni dichlorides [R(CH2PPh2)(2)]NiCl2 (R = MeN, CH2, nil) with (dppv)(CO)(2)Fe(pdt) (dppv = 1,2-C2H2(PPh2)(2), pdt = 1, 3-propanedithiolate) and NaBF4 gave dicarbonyl models {[R(CH2PPh2)(2)]-Ni(pdt)Fe(CO)(2)(dppv)}(BF4)(2) (R = MeN, [1a](BF4)(2); R = CH2, [1b] (BF4)(2); R = nil, [1c](BF4)(2)) and mu-chloro models {[R(CH2PPh2)(2)]-Ni(pdt)(mu-Cl)Fe(CO)(dppv)}(BF4) (R = MeN, [2a](BF4); R = CH2, [2b](BF4); R = nil, [2c](BF4)). Further treatment of [1a](BF4)(2)-[1c](BF4)(2) with Me3NO center dot 2H(2)O afforded mu-hydroxo models {[R(CH2PPh2)(2)]Ni(pdt)(mu-OH)Fe(CO)(dppv)}(BF4) (R = MeN, [3a] (BF4); R = CH2, [3b](BF4); R = nil, [3c](BF4)), whereas t-fluorido models {[R(CH(2)PFh(2))(2)]Ni(pdt)Fe(CO)(t-F)(dppv)}(BF4) (R = MeN, [4a](BF4); R = CH2, [4b](BF4); R = nil, [4c](BF4)) could be prepared by further treatment of [3a](BF4)-[3c](BF4) with HBF4 center dot Et2O. While first t-bicarbonato models {[R(CH2PPh2)(2)]Ni(pdt)Fe(CO)(t-OCO2H)(dppv)}(BF4) (R = MeN, [5a](BF4); R = CH2, [5b](BF4); R = nil, [5c](BF4)) were prepared by CO2 fixation reactions of [3a](BF4)-[3c](BF4) with 0.8 MPa CO2, the esterification reactions of [5a] (BF4) [5c](BF4) with MeOH or the CO2 fixation reactions of [1a](BF4)(2)-[1c](BF4)(2) with Me3NO and in situ generated CO2 in MeOH yielded the first t-carbonato models {[R(CH2PPh2)(2)]Ni(pdt)Fe(CO)(t-OCO2Me)(dppv)}(BF4) (R = MeN, [6a] (BF4); R = CH2, [6b] (BF4); R = nil, [6c](BF4)). All possible pathways for production of these new model complexes are briefly discussed, and their molecular structures were fully characterized by various spectroscopies and confirmed for some of them by X-ray crystallography.