(Dialkylamino)phosphorus Metal Carbonyls. 5. Chemical Reactivity of the Phosphorus-Bridging Carbonyl Group in Carbonylbishexacarbonyldiiron

Article abstract of DOI:10.1021/ja00217a014

Treatment of ((i-Pr)2NP)2COFe2(CO)6 with NaBH4 in methanol results in reduction of the phosphorus-bridging carbonyl group to give the corresponding secondary alcohol ((i-Pr)2NP)2CH(OH)Fe2(CO)6.Similar treatment of ((i-Pr)2NP)2COFe2(CO)6 with LiAlH4 in diethyl ether results in more extensive reduction to give a dark orange product of stoichiometry ((i-Pr)2NP)2CH2Fe2(CO)6 shown, however, by X-ray diffraction (triclinic, <*>; a=14.412(6), b=10.409(5), c=10.014(4) Angstroem; α=111.80(3), β=82.19(3) γ=106.86(4)^o; Z=2) to be ((i-Pr)2NPHCHPN(i-Pr)2)Fe2(CO)6 in which an iron-phosphorus bond has been broken and a new iron-carbon bond formed.Treatment of ((i-Pr)2NP)2COFe2(CO)6 with the alkyllithiums RLi (R=Me, n-Bu) results in addition to the phosphorus-bridging carbonyl group to give the corresponding tertiary alcohols ((i-Pr)2NP)2C(R)(OH)Fe2(CO)6.Reduction of ((i-Pr)2NP)2COFe2(CO)6>^-, which can be isolated as its orange bis(triphenylphosphine)iminium salt or as the light orange trimethyltin derivative ((i-Pr)2NP)(Me3SnP)COFe2(CO)6.Reaction of <(i-Pr)2NPCOFe2(CO)6>^- with (i-Pr)2NPCl2 results in rearrangement with expulsion of the phosphorus-bridging carbonyl group to give orange <((i-Pr)2NP)((i-Pr)2N)(Cl)PP>Fe2(CO)6.X-ray diffraction (monoclinic, P2₁/a; a=15.384(6), b=18.355(4), c=10.125(1) Angstroem; β=108.19(2)^o; Z=4) indicates a structure with a triphosphorus chain bridging an Fe2(CO)6 unit through the end phosphorus atoms.One of the end phosphorus atoms of this triphosphorus chain is an ordinary (diisopropylamino)phosphido group whereas the other end phosphorus atom is trigonal pyramidal with a lone pair.The center phosphorus atom of this triphosphorus chain is four-coordinate, being bonded to the other two phosphorus atoms, a diisopropylamino group, and a chlorine atom.Reaction of ((i-Pr)2NP)2COFe2(CO)6 with alcohols ROH (R = Me, Et) under relatively vigorous conditions results in expulsion of the phosphorus-bridging carbonyl groups to give yellow ((i-Pr)2NPOR)((i-Pr)2NPH)Fe2(CO)6.Reaction of ((i-Pr)2NP)2COFe2(CO)6 with hydrogen bromide results in expulsion of the phosphorus-bridging carbonyl group and selective cleavage of one of the diisopropylamino groups to give orange ((i-Pr)2NPBr)(HPBr)Fe2(CO)6; both stereoisomers have been detected by 31P NMR, and one has been isolated in the pure state.Reaction of ((i-Pr)2NPOEt)((i-Pr)2NPH)Fe2(CO)6 with hydrogen bromide results in selective cleavage of one of the two diisopropylamino groups to give orange ((i-Pr)2NPOEt)(HPBr)Fe2(CO)6.The formulation of this complex as a novel bis(phosphido)hexacarbonyldiiron derivative with four different terminal groups ((i-Pr)2N, EtO, H, and Br) has been confirmed by structure determination using X-ray diffraction (triclinic, <*>; a=13.700(6), b=9.818(5), c=9.258(5) Angstroem; α=64.54(4), β=96.07(4), γ=84.80(4)^o; Z=2).