Reactive Rigid-Rod Organometallic Polymers Involving Linear Triplatinum Units Connected by π-Conjugated Bisisocyanides

Axial ligand exchange reactions of [Pt3(μ-dpmp)2(XylNC)2](PF6)2 (1) with monoisocyanide
molecules afforded a series of linear triplatinum complexes, [Pt3(μ-dpmp)2(RNC)2](PF6)2 (R
= 2,4,6-mesityl (2), tert-butyl (4), 4-tolyl (5)) and [Pt3(μ-dpmp)2(XylNC)(t-BuNC)](PF6)2 (3),
which were characterized by spectroscopic, X-ray crystallographic, and absorption (EXAFS)
analyses. With the increase of π-acidity of the terminal isocyanide, the Pt−Pt bond length
became longer due to electron transfer from the Pt3 core to the isocyanide group. Terminal
ligand exchange reactions of 1 with bulky aromatic bisisocyanides (bisNCn) led to successful
isolation of the rigid-rod triplatinum cluster polymers formulated as {[Pt3(μ-dpmp)2(bisNCn)](PF6)2}n (bisNCn = 2,3,5,6-tetramethylphenylene-1,4-bisisocyanide (bisNC1) (7a), 3,3‘,5,5‘-tetramethylbisphenylene-4,4‘-bisisocyanide (bisNC2) (7b)). The structure of compound 7a,
determined by X-ray crystallography, was composed of the linear, metal−metal bonded {Pt3(μ-dpmp)2}2+ fragments (av Pt−Pt = 2.699 Å) covalently connected by the bisisocyanide
molecules, resulting in an infinite rigid-rod polymeric structure. By using less bulky
bisisocyanides, the ligand exchange reaction stopped at the formation of the triplatinum
cluster dimers [(bisNCn)Pt3(μ-dpmp)2(bisNCn)Pt3(μ-dpmp)2(bisNCn)](PF6)4 (bisNCn = phenylene-1,4-bisisocyanide (bisNC3) (8a), 2,5-dimethylphenylene-1,4-bisisocyanide (bisNC4)
(8b)), which were characterized by EXAFS analyses to involve the weakly metal−metal
bonded Pt3 fragments (av Pt−Pt = 2.85 Å). The rigid-rod polymer 7a was demonstrated to
be quite reactive even in heterogeneous systems toward H+, NO+, tetracyanoethylene (tcne),
and electron-deficient alkynes, to afford the cluster polymers formulated as {[Pt3(μ-H)(μ-dpmp)2(bisNC1)](BF4)3}n (13), {[Pt3(μ-NO)2(μ-dpmp)2(bisNC1)](BF4)4}n (14), {[Pt3(μ-C12N8)(μ-dpmp)2(bisNC1)](PF6)2}n (15), and {[Pt3(μ-R1C2R2)(μ-dpmp)2(bisNC1)](PF6)2}n (16a, R1 =
H, R2 = CO2CH3; 16b, R1 = R2 = CO2CH3). The structures of the polymers 13−16 were
estimated on the basis of the X-ray crystallographic and spectroscopic analyses for the related
reference complexes [Pt3(μ-H)(μ-dpmp)2(XylNC)2]3+ (9), [Pt3(μ-NO)2(μ-dpmp)2(RNC)2](BF4)4
(10, R = Xyl, Mes), [Pt3(μ-C12N8)(μ-dpmp)2(RNC)2](PF6)2 (11, R = Xyl, Mes), and [Pt3(μ-R1C2R2)(μ-dpmp)2(XylNC)2](PF6)2 (12, R1 = H or COOCH3, R2 = COOCH3).