N-N Bond Cleavage of Organohydrazines by Molybdenum(II)and Tungsten(II)Complexes Containing a Linear Tetraphosphine Ligand.Formation of Nitrido or Imido Complexes and Their Reactivities

摘要

The Mo(II)tetraphosphine-dihalide complexes[MoX2(kappa~4-P4)](X = Cl(2a),Br(2b);P4 = meso-o-C6H4(PPhCH2CH2PPh2)2)having uncommon trigonal-prismatic geometry cleaved the N-N bond in Me2NNH2 and PhNHNH2 at room temperature to form the nitrido complexes trans-[MoX(N)(kappa~4-P4)](X = Cl(3a),Br(3b)).In contrast,similar reactions of the W(II)congener[WBr2(kappa~4-P4)]afforded the imido complex trans-[WBr(NH)(kappa~4-P4)]~+(4c~+),which was isolated as a PF6 or BPh4 salt.Addition of HBF_4 converted 3 into the imido complexes trans-[MoX(NH)(kappa~4-P4)][BF_4](X = Cl(4a[BF_4]),Br(4b[BF_4])),while deprotonation of 4a~+ and 4b~+ by NEt_3 readily regenerated 3a and 3b.At elevated temperatures,2a also reacted with RNHNHR(R = Me,Ph),giving the corresponding organoimido complexes trans-[MoCl(NR)(kappa~4-P4)][PF6](6[PF6])after anion metathesis with K[PF6].The mechanism has been proposed for the N-N bond cleavage,which involves the proton shift in the end-on coordinated organohydrazine followed by the two-electron reduction by the M(II)center to give the M(IV)imido complex and the amine.The nitrido ligand in 3a is susceptible to electrophilic attack by methyl trifluoromethanesulfonate to form 6[CF3SO3](R = Me),while reactions of 3a with acid chlorides RCOCl(R = Me,Ph,p-tolyl(Tol))afforded the neutral acylimido complexes cis,mer-[MoCl2(NCOR)(kappa~3-P4)](7).Treatment of 7 with K[PF6]yielded the cationic complexes trans-[MoCl(NCOR)(kappa~4-P4)][PF6](8[PF6]).On the other hand,imido complex 4a[BF_4]smoothly reacted with isocyanates RNCO(R = Ph,Tol)in the presence of a catalytic amount of Et3N to give the carbamoylimido complexes trans-[MoCl(NCONHR)-(kappa~4-P4)][BF_4](9[BF_4]),and the thiocarbamoyl analogue trans-[MoCl(NCSNHPh)(kappa~4-P4)][PF6](10[PF6])was also obtained from 4a[PF6]and PhNCS.Although hydrolysis of 7(R = Tol)in a THF/aqueous KOH mixture resulted in the formation of p-toluamide only in low yield,reduction of the same complex with NaBH4 and LiAlH4 generated p-toluamide and 4-methylbenzylamine,respectively,in moderate yields.Molecular structures of 3a,4a[BF_4],4c[BPh4],6[PF6](R = Me),6[BF_4](R = Ph),7(R = Me),8[PF6](R = Me),and 9[BF_4](R = Tol)were determined crystallographically.