Cycloaddition Reactions of Terminal Alkynes and Phosphaalkynes with an Isolable 5-Coordinate β-Diiminate Platinum(IV) Dihydrosilyl Complex

Abstract

Combining (Cl-nacnac)Pt(H)(1-pentene) (Cl-nacnac = N-p-Cl-phenyl-β-diiminate) and HSiR3 (SiR3 = SiPh3, SiEt3, SiHPh2) leads to rapid displacement of 1-pentene; oxidative addition of the Si−H bond produces a stable 5-coordinate Pt(IV) silyl dihydride complex which has been isolated and characterized crystallographically. The 5-coordinate silyl dihydride platinum(IV) complex undergoes a cycloaddition reaction with either acetylene or phosphaalkyne to form a vinyl or phosphaalkenyl Pt(IV) product, respectively. One acetylenic carbon adds to the central methine carbon of the Cl-nacnac ligand and the other alkyne carbon or phosphorus coordinates to the vacant site of the d6 metal. Phosphaalkynes are polarized such that the carbon is at the negative end of the dipole; however we observe a final product that reflects a reversal of this normal polarity. The phosphorus is nucleophilic even after the cycloaddition reaction is complete, and its lone pair can be methylated by MeOTf (OTf = trifluoromethanesulfonate) or protonated by addition of HBF4·Et2O.

Stabilization of Trans Disilyl Coordination at Square-Planar Platinum Complexes

“…In the high-field region, two equally integrating 1 H NMR signals appear at δ −7.04 and −9.07 as a pseudotriplet ( 2 J H–P = 15 Hz, 1 J H–Pt = 645 Hz) and a doublet of doublets ( 2 J H–P = 170 and 25 Hz, 1 J H–Pt = 980 Hz), respectively, with coupling constants in agreement with an oxidized Pt­(IV) center (Figure ). , The difference in 1 J H–Pt indicates that the hydrides are trans to different ligands, the lowest value referring to a hydride trans to the stronger trans influence ligand. This assignment is also confirmed by the more shielded resonance displaying a large 2 J H–P = 170 Hz as a result of the trans disposition to phosphorus.…”

Solvent-Driven P–S vs P–C Bond Formation from a Diplatinum(III) Complex and Sulfur-Based Anions

“…The elimination reduction processes in hexacoordinate Pt­(IV) complexes, as well as in Pd­(IV) complexes, are known to pass through the loss of a ligand to generate a five-coordinate intermediate as a preliminary step, − and five-coordinate Pt­(IV) complexes are now well-recognized species. − The synthesis of complexes 2 – 5 can be envisaged to start with the coordination of a good nucleophile, the L ∧ S – anion, to one of the Pt­(III) centers, affording a formally Pt­(II),Pt­(IV) unsaturated complexes in which the L ∧ S – ligand is terminally bonded to Pt­(IV). The reductive coupling between a bridging diphenylphosphanido group and the organic sulfide on the Pt­(IV) center (breakdown of Pt IV –P and Pt IV –S bonds) can form the new PPh 2 SL group while one of the initial two pairs of nonbonding electrons of the S center can give rise to a new Pt II –S bond.…”

N-Aryl β-diiminate complexes of the platinum metals

“…With alkynes, they undergo initial insertion in the Pt-H bond, followed by C-C coupling or C-H activation reactions. 37 With silanes they give complexes L H Pt(silyl)H 2 , 36 which are rigid on the NMR timescale. These bind PMe 3 weakly, and also react with acetylene and phospha-alkynes to produce tricyclic complexes analogous to the Ru cyclo-adducts mentioned above (but not reversibly in this case).…”

“…This complex is rather reactive and undergoes H/D exchange with deuterated solvents (C 6 D 6 , C 6 D 5 CD 3 ) where not only the hydride positions but also the ligand i Pr groups incorporate Scheme 12 C-H and Si-H activation by in situ generated L H Pt II Me. [34][35][36][37] Scheme 13 Benzene activation and COD insertion at in situ generated L Me Pd II Me. 38 Scheme 14 Formation and reactivity of L iPr Ir I (COE)(N 2 ).…”