Coupling of Alkynes Mediated by [RuCp(PPh₂NHPh)(CH₃CN)₂]⁺:  Formation of η⁴-Butadiene Amido Complexes through Migration and N−H Activation of the PPh₂NHPh Ligand

Abstract

This is a continuation of our work on the reactions of [RuCp(PR 3 )(CH 3 CN) 2 ]PF 6 with terminal alkynes and diynes. Here now we use, instead of PR 3 , the phosphino-amine ligand PPh 2 NHPh. The reaction pattern is found to be similar except that the N-H bond of the phosphine ligand is activated and not a C-H bond as before. Thus the reaction of [RuCp(PPh 2 NHPh)(CH 3 -CN) 2 ]PF 6 with HCtCR (R ) Ph, n-Bu, CH 2 Ph), 1,6heptadiyne, and 1,7-octadiyne results in the formation of the η 4 and [RuCp(η 4 -C 4 H 3 (CH 2 ) 4 -PPh 2 -κ 1 -(N)-NPh)]PF 6 in good yields.

C–H vs. N–H Bond Activation in Aminophosphane Ligands: Reaction of [Cp*Ru(MeCN)2(PR12NHR2)]+ (R1 = Ph, iPr; R2 = Ph, C6F5) with Alkynes

“…[7] However, we have found that in certain cases a different reaction pathway that leads to products other than amidobutadiene complexes is feasible.…”

“…[7] One of the most distinctive spectral features of these complexes is the resonance for H 1 [°] with estimated standard deviations in parentheses: Ru1-C2 2.182(2), Ru1-C3 2.188(2), Ru1-C4 2.210(2), Ru1-C1 2.218(2), Ru1-C5 2.245(2), Ru1-N1 2.164(1), Ru1-C11 2.244(2), Ru1-C12 2.216(2), Ru1-C13 2.223 (2), Ru1-C16 2.217(2), P1-C16 1.766(2), C11-C12 1.401(3), C12-C13 1.420(3), C13-C16 1.413(3), N1-P1 1.599(2); Ru1-N1-P1 96.89(7), N1-Ru1-C16 72.30(7), N1-P1-C16 100.23 (8), C11-C12-C13 128.1(2), C12-C13-C16 129.5(2). [7] The dimensions of the butadiene fragment are consistent with the delocalization of the double bonds, matching the values reported for the cyclopentadienyl complexes. The Ru1-N1 separation of 2.242(3) Å in 2a is significantly longer than the corresponding Ru-N bond lengths observed in 1a and in the cyclopentadienyl derivatives.…”

“…If the addition of the second alkyne ligand is fast, then the resulting 18-electron bis(alkyne) complex undergoes oxidative alkyne coupling to yield a ruthenacyclopentatriene complex, and the course of the reaction would be as described previously. [1,7] However, in certain cases involving systems containing the strong electron-releasing aminophosphane iPr 2 PNHPh, the metal center in the 16-electron intermediate is electron-rich enough to activate one C-H bond in the ortho-position of the phenyl ring to yield an orthometalated hydrido complex as a result of the oxidative addition reaction. This Ru IV species is most likely in dynamic equilibrium with the 16-electron complex.…”

“…Very recently, Kirchner and co-workers have reported the activation of alkynes by the aminophosphane complex [CpRu(MeCN) 2 (PPh 2 NHPh)] + , which results in the formation of η 4 -amidobutadiene complexes. [7] In this case phosphane migration also occurs, and is followed by an N-H bond activation process in the amino group rather than C-H bond activation.…”

Reactions of Ruthenium–Aminophosphane Complexes with Diynes: P–N Bond Activation and Formation of Novel Phosphaallyl, Azaallyl, and Aminocarbene Complexes

“…[8] Complexes of the types [RuCp(PPh 2 NHPh)-(CH 3 CN) 2 ] + and [RuCp*(PR 2 NHRЈ)(CH 3 CN) 2 ] + (R = Ph, iPr, RЈ = Ph, C 6 F 5 ) have been found to react with terminal alkynes and diynes to give amido butadiene complexes. [9,10] In all these reactions, the N-H bond but not the P-N bond is cleaved unless larger amounts of water are present. Recently, when we switched over to a complex where the aminophosphane lacks a N-H bond viz.…”