Transition metal chemistry of cyclodiphosphanes containing phosphine and amide-phosphine functionalities: Formation of a stable dipalladium(II) complex containing a Pd–P σ-bond.

Abstract

Cyclodiphosphazanes containing phosphine or phosphine plus amide functionalities {(^tBuNP(OC₆H₄PPh₂-o)}₂ (3), {^tBuNP(OCH₂CH₂PPh₂)}₂ (4), {^tBuHN(^tBuNP)₂OC₆H₄PPh₂-o} (5), and {^tBuHN(^tBuNP)₂OCH₂CH₂PPh₂} (6) were synthesized by reacting cis-{^tBuNPCl}₂ (1) and cis-[^tBuHN(^tBuNP)₂Cl] (2) with corresponding phosphine substituted nucleophiles. The reactions of 3 and 5 with excess of elemental sulfur or selenium produce the corresponding tetra and trichalcogenides, {(^tBuNP(E)(OC₆H₄P(E)Ph₂-o)}₂ (7, E = S; 8, E = Se) and {^tBuHN(^tBuNP)₂OC₆H₄P(E)Ph₂-o} (9, E = S; 10, E = Se), respectively, in quantitative yields. The reactions between 3 and [Rh(COD)Cl]₂ or [M(COD)Cl]₂ (M = Pd or Pt) afford bischelated complexes [Rh(CO)Cl{^tBuNP(OC₆H₄PPh₂-o)}]₂ (11), and [MCl₂{^tBuNP(OC₆H₄PPh₂-o)}]₂ (12, M = Pd; 13, M = Pt) in good yield. The 1 : 2 reaction between 3 and [PdCl(η³-C₃H₅)]₂ in dichloromethane resulted initially in the formation of a tripalladium complex of the type [Pd₃Cl₄(η³-C₃H₅)₂{^tBuNPOC₆H₄PPh₂}₂] (14a) which readily reacts with moisture to form an interesting binuclear complex, [Cl₂Pd{μ-(PPh₂C₆H₄OP(μ-^tBuN)₂P(O)}(μ-Cl)Pd(OC₆H₄PPh₂)] (14b). One of the palladium(II) atoms forms a simple six-membered chelate ring, whereas the other palladium(II) atom facilitates the moisture assisted cleavage of one of the endocyclic P–O bonds followed by the oxidation of P(III) to P(V) thus forming a Pd–P σ-bond. The broken ortho-phosphine substituted phenoxide ion forms a five-membered palladacycle with the same palladium(II) atom. Similar reaction of 5 with [PdCl(η³-C₃H₅)]₂ also affords a binuclear complex [{PdCl(η³-C₃H₅)}^tBuNH{^tBuNP}₂OC₆H₄PPh₂{PdCl₂}] (15) containing a PdCl₂ moiety which forms a six-membered chelate ring via ring-phosphorus and PPh₂ moieties on one side and a PdCl(η³-C₃H₅) fragment coordinating to amide bound phosphorus atom on the other side of the ring. Treatment of 3 with four equivalents of AuCl(SMe₂) produces a tetranuclear complex, [(AuCl)₄{^tBuNP(OC₆H₄PPh₂)}₂] (16), whereas a 1 : 3 reaction between 5 and AuCl(SMe₂) leads to the formation of a trinuclear complex, [^tBuNH{^tBuNP(AuCl)}₂OC₆H₄P(AuCl)Ph₂] (17). The crystal structures of 3, 5, 9–11 and 13–17 are reported.