Site-Selective Incorporation of Zerovalent Platinum and Palladium Fragments into Diplatinum Centers Supported by a Triphosphine Ligand

Abstract

Reaction of [Pt2(RNC)6](PF6)2 (R = 2,6-xylyl (Xyl) (a) and 2,4,6-mesityl (Mes) (b)) with 2 equiv of bis((diphenylphosphino)methyl)phenylphosphine (dpmp) afforded a mixture of isomeric diplatinum complexes, syn-[Pt2(μ-dpmp)2(RNC)2](PF6)2 (1) and anti-[Pt2(μ-dpmp)2(RNC)2](PF6)2 (2), which were purified by cycles of recrystallization and were characterized by X-ray crystallography. Complexes 1 and 2 consist of a diplatinum core (Pt−Pt = 2.7094(8) Å (1a) and 2.683(2) Å (2a)) asymmetrically bridged by two dpmp ligands. The central phosphorus atoms of the dpmp ligands coordinate to the same metal center in the syn-dimer (1) and to different metal centers in the anti-dimer (2). Complexes 1 and 2 were fluxional in solution through symmetrical structures of syn-1‘ and anti-2‘, respectively, in which two terminal phosphine units are uncoordinated. At reflux in CH3CN or by treatment with [Cu(CH3CN)4](PF6), complexes 1a and 2a lost one isocyanide molecule to be transformed into syn-[Pt2(μ-dpmp)2(XylNC)](PF6)2 (3, Pt−Pt = 2.6834(8) Å) and anti-[Pt2(μ-dpmp)2(XylNC)](PF6)2 (4, Pt−Pt = 2.7150(7) Å), respectively. Reactions of the syn-dimer (1) with [M3(XylNC)6] readily afforded the linearly ordered trinuclear clusters, linear-[Pt2M(μ-dpmp)2(XylNC)2](PF6)2 (M = Pt (5), Pd (6)). The additional zerovalent metal atom is incorporated into the terminal position of the trinuclear aggregation, resulting in a d9−d10−d9 configuration via one electron transfer from the additional metal to the diplatinum core. The three metal atoms are joined by two metal−metal σ-bonds (average Pt−Pt = 2.724(2) Å (5), Pt−Pt/Pd = 2.690(1) Å) and are symmetrically bridged by two dpmp ligands, to form a linearly ordered trinuclear structure (Pt−Pt−M = 178.66(8)° (5), 180.0° (6)). The similar reactions of the anti-dimer (2) with [M3(RNC)6] led to a formation of the A-frame trinuclear clusters, A-frame-[Pt2M(μ-dpmp)2(RNC)2](PF6)2 (7, M = Pt, R = Xyl; 8, M = Pd, R = Mes). The three metal atoms are joined by two metal−metal bonds (Pt−M = 2.6039(7) Å (7), 2.599(3) Å (8)) and asymmetrically bridged by two dpmp ligands, resulting in a so-called trimetallic A-frame structure (Pt−M−Pt = 76.76(3)° (7), 78.5(1)° (8)). The additional metal is trapped into the middle position of the trinuclear core, through the insertion of d10 ML2 fragment into the Pt−Pt σ-bond, which is interestingly contrasted with the terminal position observed in the reactions of the syn-dimer.

Linear Triplatinum Tetrahydride Complex Supported by Triphosphine Ligands, [Pt3(µ‐H)2(H)2(µ‐dpmp)2](BF4)2 {dpmp = bis(diphenylphosphinomethyl)phenylphosphine}

“…The complex cation possesses a crystallographically imposed inversion center at Pt2 and consists of linearly ordered trinuclear Pt centers supported by two dpmp ligands [Pt1–Pt2 2.8021(2) Å, Pt1–P1 2.276(2) Å, Pt1–P3* 2.280(2) Å, Pt2–P2 2.291(2) Å, Pt1–Pt2–Pt1* 180°, P1–Pt1–P3* 168.42(8)°, P2–Pt2–P2* 180°]. The Pt1–Pt2 distance of 2.8021(2) Å is significantly longer than usual Pt–Pt σ bonds, for example, 2.723(2) and 2.724(2) Å in 1a ,, and is suggestive of the presence of a bridging hydride between the two neighboring platinum (Pt1/Pt1* and Pt2) centers. Nevertheless, it is appreciably shorter than the Pt–Pt distances in [Pt 3 (µ‐H)(µ‐dpmp) 2 (XylNC) 2 ](BF 4 ) 3 [2.8680(6) Å] and [Pt 2 Me 2 (µ‐H)(µ‐dppm) 2 ](PF 6 ) [2.932(1) Å, dppm = bis(diphenylphosphanyl)methane], which involve phosphine‐bridged Pt(µ‐H)Pt units , …”

“…In the course of developing low‐valent “extended metal atom chains (EMACs)”, we have studied transition‐metal complexes supported by linear tri‐ and tetraphosphine ligands, bis(diphenylphosphinomethyl)phenylphosphine (dpmp) and meso ‐ and rac ‐bis[(diphenylphosphinomethyl)phenylphosphanyl]methane (dpmppm), which are intended to be utilized as linearly incremental metal building blocks . During our studies, linear trinuclear complexes, [Pt 2 M(µ‐dpmp) 2 (XylNC) 2 ](PF 6 ) 2 {M = Pt ( 1a ), Pd ( 1b ); Xyl = 2,6‐xylyl}, were synthesized (Scheme ) and have proven to be good building blocks for further extended metal strings . Complexes 1a and 1b undergo reductive coupling to afford linear Pt 2 M 2 Pt 2 complexes, [Pt 4 M 2 (µ‐H)(µ‐dpmp) 4 (XylNC) 2 ] 3+ {M = Pt ( 2a ), Pd ( 2b )}, in which a hydride bridges the central two M centers (M = Pt, Pd) to connect two trinuclear building blocks as a Pt 2 M–H–MPt 2 linear structure (Scheme ) .…”

New trimetallic sandwich complexes of platinum(0) and palladium(0)

“…This synthesis offers an avenue to the synthesis of a range of substituted triplatinum tropylium complexes which will be of use for future studies of the catalytic and material properties. The work of Tanase and coworkers suggests potential methods for the isolation of the individual mixed-metal complexes [18], and additional studies are underway to extend this chemistry to other metals.…”

Hexapalladium cluster: Unique cluster construction reaction of cyclic Pd3(CNC6H3Me2-2,6)6 and linear [Pd3(CNC6H3Me2-2,6)8]2+

“…We have been intrigued by the insertion reaction of metal fragments into the metal-metal bonded clusters as an ideal synthetic method for constructing metal-metal bonded polynuclear complexes [6]. It is well known that one metal fragment of d 10 transition metals can be inserted into the M(I)-M(I) bond of dinuclear complexes (M = Pt and Rh) to form heterotrinuclear A-frame complexes: [Pt 2 Pd(l-dpmp) 2 -(CNMes) 2 ] 2+ [7], [Pt 2 (l-HgCl 2 )Cl 2 (l-dppm) 2 ] [8], and [(CpRh) 2 (l-AuPPh 3 )(l-CO)(l-dppm) 2 ] + [9] have been synthesized by the insertion reactions of Pd(CNMes) 2 , HgCl 2 , and [AuPPh 3 ] + into the corresponding Pt 2 and Rh 2 complexes, respectively. In the case of homoleptic palladium isocyanide complexes, although many di-, tri-, and multinuclear complexes with isocyanide ligands have been prepared by electrochemical reaction of metal ions in different formal oxidation states [10][11][12][13][14][15][16], such an insertion reaction of a 'Pd 0 (CNMe) 2 ' fragment into a dicationic dipalladium complex [Pd 2 (CNMe) 6 ] 2+ with d 9 configuration has been successfully applied to yield the linear tripalladium complex [Pd 3 (CNMe) 8 [13g].…”