Assembling Metal Clusters with Covalent Linkers: Synthesis and Structure of a Quasi‐Planar Pt₁₈ Dendrimer Containing Five Clusters Connected by σ‐Alkynyl Spacers

Abstract

Transition-metal s-alkynyl derivatives [1] are emerging as potentially useful precursors for advanced materials due to their promising magnetic, [2] liquid-crystalline, [3] nonlinear optical, [4] and luminescence [5] properties. Moreover, there is considerable and increasing interest for their application in the synthesis of metal-containing macrocyclic, [6] dendritic, [7] and rigid-rod molecular frameworks with delocalized p systems. These compounds include derivatives of various dimensions, actively investigated for their potential use in molecular electronics, [8,9] and contain isolated metal centers either located at the extremes [8][9][10][11] or regularly intercalated [8,12] into the main chain. Ordered structures with alternated metal clusters (or metal-metal-bonded bimetallic units [13] ) and conjugated s-alkynyl spacers [14][15] are extremely rare, [16] although of great potential interest. [10] This may be due to: 1) the tendency of metal clusters to undergo fragmentation or condensation, 2) their multiple and undistinguishable reactive positions, which facilitate the formation of complex mixtures of products, and 3) the preferred p interaction between the cluster and the alkynyl units [1,17] (the metal-alkynyl s linkage usually results in increased electronic delocalization [9] ). In this paper we show that tri-and hexanuclear platinum clusters with sizable bridging phosphide groups are suitable precursors to ordered materials. Indeed, the bulky PtBu 2 ligands in [Pt 3 (m-PtBu 2 ) 3 (L) 2 (X)]n+ [18] and [Pt 6 (m-PtBu 2 ) 4 -(CO) 4 (X) 2 ]2n+ [19] (X = neutral ligand, n = 1; X = monoanionic ligand, n = 0; L = neutral ligand) impart remarkable thermal and chemical stability to the {Pt x (m-P) y } cores and leave a limited number of reactive sites properly positioned to build ordered structures. Moreover, they force alkynyl ligands to bind the polynuclear system with s,h 1 -rather than p,h 2 -interactions.[20] Several structures with predefined molecular shape can therefore be engineered through the combination of these building blocks with well-chosen s-alkynyl spacers, one of which is shown in Scheme 1. The trinuclear precursor Scheme 1. Synthesis of complex 6. i) 1,3,5-C 6 H 3 (CCH) 3 , CuI, NEt 2 H, 25 8C, 24 h (80 %); ii) 3 (2 equiv), 5, CuI, NEt 2 H, 25 8C, 24 h (85 %) (5 = [Pt 6 (m-PtBu 2 ) 4 (CO) 4 Cl 2 ]).

21 Organometallic chemistry of bi- and poly-nuclear complexes

“…74,75 1,3,5-Triethynyl benzene has been used in the construction of dendritic platinum complexes containing up to 18 platinum centres. 76 8 Copper, silver, gold The dinuclear species absorb strongly at ca. 260-300 nm [phosphine (p-p*) transitions] with lower intensity absorptions at lower energies (300-400 nm) most likely arising from metal perturbed alkynyl p-p* transitions.…”

Organometallic Complexes for Nonlinear Optics, 47 – Synthesis and Cubic Optical Nonlinearity of a Stilbenylethynylruthenium Dendrimer

“…Parallel to this development, the number of reports of dendrimers, monodisperse macromolecules with a hyperbranched topology, has also undergone an exponential increase 3, 4. Metal‐containing dendrimers have consequently commanded ever‐increasing attention, with the vast majority thus far comprising a saturated organic branched structure with organometallic or coordination complex metal centers at the periphery; examples with metal atoms in each generation level, and with a π‐delocalizable structure, are comparatively rarer 5, 6. Amongst the extant examples of the latter, metal alkynyl dendrimers have attracted especial attention, with studies focusing on inter alia their photophysical and nonlinear optical (NLO) properties 7–12…”

A molecular wire incorporating a robust hexanuclear platinum cluster

“…The dication {Pt 6 }(CO) 2 2+ readily undergoes substitution of two terminal carbonyl ligands on the peripheral Pt atoms, to give {Pt 6 }L 2 x+ (x = 2, L = inter alia RNC, RCN, PMe 3 ; x = 0, L = Cl [1], I). 7 The {Pt 6 } cluster unit is stable enough to permit the synthesis of multicluster dendrimers with s-alkynyl spacers, 8 and alternating cluster-phenyleneethynylene oligomers, 9,10 by Cu(I)-mediated reaction of 1 with terminal alkynes. Such supramolecular metal cluster systems could be of interest in molecular-scale electronics, providing that they can be shown to be stable enough to be incorporated intact into devices.…”