{Bis[2-(diphenylphosphanyl)ethyl]phenylphosphane-κ3 P,P′,P′′}[(Z)-8-mesitylcyclooct-4-en-1-yl]platinum(II) tetrafluoridoborate dichloromethane disolvate

In the title ionic compound, [Pt(C17H23)(C34H33P3)](BF4)·2CH2Cl2, the PtII atom adopts a square-planar coordination geometry with the large (Z)-8-mesitylcyclooct-4-en-1-yl group occupying the fourth coordination site. The (triphos)Pt moiety and the mesityl group are attached to the cyclooct-4-ene motif at the 1- and 8-position in a syn configuration. The (BF4)− anion and one of the dichloromethane solvate molecules each are disordered over two sets of sites.

In the title ionic compound, [Pt(C 17 H 23 )(C 34 H 33 P 3 )](BF 4 )Á-2CH 2 Cl 2 , the Pt II atom adopts a square-planar coordination geometry with the large (Z)-8-mesitylcyclooct-4-en-1-yl group occupying the fourth coordination site. The (triphos)Pt moiety and the mesityl group are attached to the cyclooct-4-ene motif at the 1-and 8-position in a syn configuration. The (BF 4 ) À anion and one of the dichloromethane solvate molecules each are disordered over two sets of sites.
The NIH

Comment
Migratory insertion of metal-carbon (M-C) bond into alkenes is the cornerstone of many transition-metal catalyzed C-C bond forming processes such as Ziegler-Natta polymerization and the palladium catalyzed Heck type couplings. Mechanistically, a migratory insertion process involves incipient development of a bond between the metal and an alkene carbon via a planar four-center transition state, which qualitatively renders the β-carbon positively charged with the carbon bound to the metal being negatively charged, and subsequent carbon migration from the metal to the β-carbon to formally furnish both a new C-C and a new M-C bond. The strength of the M-C bond significantly affects the kinetics of the insertion process, with the reaction rate drastically decreasing with increasing M-C bond strength. M-C bonds for the third-row late transition metals especially Ir and Pt are reluctant towards migratory insertion reactions because of their high bond strength. In contrast to the ease of Ni-C and Pd-C in participating migratory insertions, to our knowledge, examples for their heavier congener Pt remain exceptionally rare, with the reaction generating the title compound herein representing a rather intriguing case of Pt-C migratory insertion reactions enabled by ligand coordination.
The structure of the cationic moiety of the title compound is shown in Fig. 1, with selected bond length and angles listed in Table 1. The Pt II center is four-coordinate, with triphos acting as a tridentate ligand and the large 8-mesitylcyclooct-4Zen-1-yl group occupying the 4t h coordination site of the Pt center. The Pt1-C1 bond is measured to be 2.166 (2) Å in length, similar to previously reported triphos-chelating Pt II -alkyl compounds [Koh et al. (2004); Feducia et al. (2008);Sokol et al. (2011)]. The three Pt-P bonds all show a bond length around 2.3 Å, with P2-Pt1-P1 and P3-Pt1-P2 bond angles being 82.86 (2) o and 83.98 (2) o , respectively. While the C1-C2 bond shows a length [1.553 (3) Å] common for a C-C single bond, the C5-C6 bond exhibits a length [1.328 (4) Å] most typical for a C=C double bond. It is also clear that the mesityl group and the Pt moiety are cis-to each other while both attaching to the cyclooct-4Z-ene motif. This configuration is in good agreement with the mechanistically predicted Pt-mesityl to COD migratory insertion product.
One of the unit cell packing diagrams for the title compound is shown in Fig. 2. The solvent molecules and the BF 4 anion reside in small cavities created by columns of the staked cationic Pt II moiety.

Experimental
The title compound was obtained unexpectedly while attempting to synthesize [(triphos)Pt-mesityl](BF 4 ) via the ligand metathesis reaction between triphos and (COD)Pt(mesityl)(I): A mixture of triphos (0.15 g, 0.28 mmol) and (COD)Pt(mesityl)(I) (0.15 g, 0.27 mmol) in 5 ml dry CH 2 Cl 2 was stirred under N 2 for 2 h at room temperature. An aqueous solution of NaBF 4 (0.25 g, 2.3 mmol, in 5 ml H 2 O) was added, the resulting mixture was stirred for 15 min. After separation of the organic layer, extraction with CH 2 Cl 2 (5 ml x 2) and removal of the solvent, the residue was purified by flash supplementary materials sup-2 chromatography on silica gel using CH 2 Cl 2 /MeNO 2 (1: 1) as the eluent to afford the title compound as a white solid (40% yield). Colorless crystals were obtained by slow evaporation of a CH 2 Cl 2 /hexanes mixed solution.

Refinement
All non-hydrogen atoms were refined anisotropically. The BF 4 anion was disordered, wherein the disordered fluoride atoms were refined in parts, each with their corresponding occupancy. The chloride atom of one methylene chloride molecule was disordered in two parts, each assigned 50% occupancy. The H atoms on C1 and C17 were located from difference Fourier maps and refined with H as riding atom (U iso = 1.2(C)). All the other H atoms were placed in geometrically calculated positions, with C-H = 0.95 (aromatic), 0.99 (CH 2 ), and 0.98 (CH 3 ) Å, and refined as riding atoms, with U iso (H) = 1.5U eq C (CH 3 ) or 1.2U eq C (other C), and the methyl groups were refined with AFIX 137, which allowed the rotation of the methyl groups whilst keeping the C-H distances and X-C-H angles fixed. The two hydrogen atoms of the disordered methylene chloride molecule were not added.    Bruker, 1999) h = −12→12 Least-squares matrix: full H atoms treated by a mixture of independent and constrained refinement