The Mo(II) tetraphosphine−dihalide complexes [MoX2(κ4-P
4)] (X = Cl (2a), Br (2b); P
4 = 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)(κ4-P
4)] (X
= Cl (3a), Br (3b)). In contrast, similar reactions of the W(II) congener [WBr2(κ4-P
4)] afforded the
imido complex trans-[WBr(NH)(κ4-P
4)]+ (4c
+
), which was isolated as a PF6 or BPh4 salt. Addition of
HBF4 converted 3 into the imido complexes trans-[MoX(NH)(κ4-P
4)][BF4] (X = Cl (4a[BF4]), Br
(4b[BF4])), while deprotonation of 4a
+
and 4b
+
by NEt3 readily regenerated 3a and 3b. At elevated
temperatures, 2a also reacted with RNHNHR (R = Me, Ph), giving the corresponding organoimido
complexes trans-[MoCl(NR)(κ4-P
4)][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)(κ3-P
4)]
(7). Treatment of 7 with K[PF6] yielded the cationic complexes trans-[MoCl(NCOR)(κ4-P
4)][PF6] (8[PF6]).
On the other hand, imido complex 4a[BF4] 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)(κ4-P
4)][BF4] (9[BF4]), and the thiocarbamoyl analogue trans-[MoCl(NCSNHPh)(κ4-P
4)][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[BF4], 4c[BPh4], 6[PF6] (R = Me), 6[BF4] (R = Ph), 7 (R = Me), 8[PF6]
(R = Me), and 9[BF4] (R = Tol) were determined crystallographically.
