Synthetic, Structural, Spectroscopic, and Theoretical Studies of Structural Isomers of the Cluster Pt₃(μ-PPh₂)₃Ph(PPh₃)₂. A Unique Example of Core Isomerism in Phosphine Phosphido-Rich Clusters

Abstract

Two isomers of the phosphido-bridged platinum cluster Pt(3)(&mgr;-PPh(2))(3)Ph(PPh(3))(2) (2 and 3) have been isolated, and their structures have been solved by single-crystal X-ray diffraction. Compound 2 crystallizes in the orthorhombic space group Cmc2(1) with a = 22.192(10) Å, b = 17.650(9) Å, c = 18.182(8) Å, and Z = 4. Compound 3 crystallizes with 2 molecules of dichloromethane in the monoclinic space group C2/c with a = 21.390(10) Å, b = 18.471(9) Å, c = 19.021(11) Å, beta = 105.27(5) degrees, and Z = 4. The two isomers differ essentially in their metal-metal distances and Pt-(&mgr;-PPh(2))-Pt angles. Thus 2, having an imposed C(s) symmetry, contains a bent chain of metal atoms with two short Pt-Pt distances of 2.758(3) Å and a long separation of 3.586(2) Å. In 3, which has an imposed C(2) symmetry, the metal atoms form an isosceles triangle with two Pt-Pt distances of 2.956(3) Å and one of 3.074(4) Å. These isomers can be smoothly interconverted by changing the crystallization solvents. Solution and solid-state (31)P NMR studies have been performed in order to assign the resonances of the different P nuclei and relate their chemical shifts with their structural environments. Raman spectroscopy was used to assign the nu(Pt-Pt) modes of the two structural isomers. Theoretical studies based on extended Hückel calculations and using the fragment molecular orbital approach show that the isomer with the three medium Pt-Pt distances is slightly more stable, in agreement with earlier theoretical predictions. Cluster core isomerism remains a rare phenomenon, and the present example emphasizes the role and the importance of flexible phosphido bridges in stabilizing clusters as well as the unprecedented features which can be observed in phosphine phosphido-rich metal clusters.

A New Strategy for the Preparation of Metallaboranes − Solvothermal Synthesis and Structural Characterisation of Two Nido 11‐vertex Diplatinaundecaborane Clusters

“…These are the first examples of nido 11-vertex diplatinaundecaborane clusters in metallaborane chemistry characterised by X-ray diffraction. There is a PPh 2 group bridging two Pt atoms and the PtϪPt distances [2.6672(11) Å for 1, 2.6357(8)Å for 2] are shorter than the PtϪPt distances in the diplatinaborane [(PMe 2 Ph) 3 ClPt 2 B 10 H 9 (PMe 2 Ph)] (2.863Å ) [10] and considerably shorter than the PtϪPt distances in [Pt 3 (µ-PPh 2 ) 3 Ph(PPh 3 ) 2 ] [11] (average 3.0744Å ) which also has a PPh 2 group as a bridging ligand. The Pt (7)ϪP (1) and Pt(8)ϪP(1) bond lengths are 2.314(4) Å in 1 and 2.2992(10) Å in 2, and 2.299(4) Å in 1 and 2.3013(13) Å in 2, respectively.…”

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

“…Addition of H 2 O (5 mL) caused the precipitation of 2 as a microcrystalline brown solid (720 mg, 98 %). Elemental analysis calcd (%) for C 26 .…”

The Chemical Record—A Historical Commentary

“…[19] Many more examples of serendipitous, exciting (at least for us!) findings could be given, but I have reached the upper limit of the space offered, such as the first examples of reversible CO2 fixation by a transition-metal complex fully characterized by X-ray diffraction and shown to occur by reversible carbon-carbon bond formation (Scheme 2), [20] still a topical area more than 30 years later, and its application to the catalytic lactone synthesis by telomerization of butadiene and CO2; [21] the discovery of a bridging behaviour for trialkoxysilyl ligands (-Si(OR)3) and their possible dynamic behaviour, [22] which provided an extension of the concept of hemilability to dinuclear complexes (Scheme 3); [23] the first example of migration of a silyl ligand from one metal to another in a heterometallic complex (Scheme 4); [24] the synthesis of the first molecular cyanometallate cage, [(OC)Pd(CN)Mn(C5H4Me)(CO)2]4 containing a meso arrangement of helical units (Scheme 5); [25] a remarkable example of crystallization solvent induced core isomerism in the phosphine, phosphido-rich cluster [Pt3(μ-PPh2)3Ph(PPh3)2] resulting in a change of the metalmetal distance by more than 0.5 Å; [26] the synthesis of unprecedented quinonoid zwitterions (Scheme 6), [27] which have led to a very rich coordination chemistry and most fruitful collaborations with physicists; [28] and the characterization of a triply bridging bonding mode for a cyclopentadienyl ligand in a palladium cluster (Scheme 7). [29] It has also been rewarding to see that rational approaches to molecular design have been successful and that predictions could be verified later, such as that concerning the possibility of a bridging behaviour of phosphine ligands, made in 1989, [30] and realized by H. Werner in 2000.…”

“…Quinonoid zwitterions with a large dipole moment (10 D). [26] Scheme 7. Coordination of a C5H5 ligand in a μ3-η 1 :η 2 :η 2 mode to the [Pd3] 4+ triangular subunit of the mixed-valence [Pd3 II (μ-OAc)4(μ3-Cp)Pd 0 (η 5 -Cp)] cluster.…”