Synthesis and reactivity of bis(diphenylphosphino)amine-bridged heterobimetallic iron–platinum μ-isonitrile and μ-aminocarbyne complexes

• Heterobimetallic isonitrile and μ-aminocarbyne Fe–Pt complexes have been synthesized.
• The bonding mode of the CNR ligand (bridging vs. terminal) depends on the σ-donor/π-acceptor propensity of R.
• Regioselective substitution of PPh3 at the Pt center.
• Zwitterionic compounds were obtained by deprotonation of the dppa ligand.
• Heterotrimetallic aminocarbynes were characterized by multinuclear NMR techniques and X-ray diffraction.

Reaction of [(OC)3Fe(μ-CO)(μ-dppa)Pt(PPh3)] (1) (dppa = bis(diphenylphosphino)amine) with various isonitriles in a 1:1 or 1:2 ratio yields the isonitrile-bridged compounds [(OC)3Fe(μ-CN-R)(μ-dppa)Pt(PPh3)] (2) and [(OC)2(RNC)Fe(μ-CN-R)(μ-dppa)Pt(PPh3)] (3), respectively. However, addition of tert-butylisonitrile to 1 affords the carbonyl-bridged complex [(OC)2(tert-BuNC)Fe(μ-CO)(μ-dppa)Pt(PPh3)] (2g). Upon treatment of [(OC)3Fe(μ-CN-o-anisyl)(μ-dppa)Pt(PPh3)] (2b) with SO2, the μ-CNR ligand is chased from its bridging position to give the sulfur dioxide-bridged compound [(OC)2(o-anisylNC)Fe(μ-SO2)(μ-dppa)Pt(PPh3)] (4). These compounds are converted to the μ-aminocarbyne salts [(OC)2(L)Fe{μ-CN(R)R’}(μ-dppa)Pt(PPh3)]+ (5 R’ = Me, Et) by N-alkylation using [Me3O][BF4] or ethyl triflate as electrophiles. In function of the sterical crowding exerted by μ-aminocarbyne groups, two stereoisomers can be formed. Upon addition of P(OMe)3 or tert-BuNC to 5, no carbonyl substitution occurs. Instead the Pt-bound PPh3 ligand is replaced by L′ in a regioselective manner to give [(OC)2(L)Fe{μ-CN(Me)R}(μ-dppa)Pt(L′)][BF4] (5e, 5f, 5g). Deprotonation of the N–H function of the bis(diphenylphosphino)amine ligand of salts 5 by KSi(OMe)3 or KH produces the zwitterionic compounds [(OC)2(L)Fe{μ-CN(R)R’}(μ-Ph2PNPPh2)Pt(PPh3)] (6). The latter react with various organic and inorganic electrophiles to produce the N-alkylated or metallated aminocarbyne complexes [(OC)2(L)Fe{μ-CN(R)R’}{μ-Ph2PN(E)PPh2}Pt(PPh3)]+ (7: E = Me, 8: E = AuPPh3, CuAsPh3, CuPPh3, HgMe). The molecular structures of 2c, 3b, 5b, 8a and 8b have been determined by X-ray diffraction studies.

Zwitterionic heterobimetallic aminocarbyne complexes [(OC)2(L)Fe{μ-CN(R)R’}(μ-Ph2PNPPh2)Pt(PPh3)] (L = CO, CNR) have been synthesized by deprotonation of the bridging dppa ligand and their reactivity towards various electrophiles has been investigated. Thus, N-alkylated or N-metallated aminocarbyne complexes such as the heterotrinuclear gold-amide complex [(OC)3Fe{μ-CN(Me)xylyl}{μ-Ph2PN(AuPPh3)PPh2}Pt(PPh3)][OSO2CF3] have been obtained.Figure optionsDownload as PowerPoint slide