Preparation and X-ray crystallographic determination of the structure of the platinacyclobutenone [(C6H5)3P]2Pt[OC3(C6H5)2]

Abstract

The reaction of diphenylcyclopropenone with tetrakis(triphenylphosphine)platinum(O) is described, and the results of an X-ray crystallographic study of the product are reported.

Unsupported boron–carbon σ-coordination to platinum as an isolable snapshot of σ-bond activation

“…S7), found to be 5.5 kcal mol − 1 less stable than 2. The calculated methylenecyclopropene model 3 matched the literature structures of platinacyclobutene complexes with a completely broken C-C bond (calcd: 2.239 Å; literature: 2.15-2.24 Å) and coplanar arrangement of the Pt-C-C and C-C-C planes (angle between planes: 176.9) [41][42][43] . The difference between the calculated geometries of 2 and 3 are also apparent from the Wiberg bond indices of the bonds between the cyclic fragment and the Pt, with the B-C bond of 2 (WBI: 0.54) being much more complete than the C-C bond of 3 (WBI: 0.10).…”

“…This butterfly structure provides a clear indication that 2 does not fit a 'metallacyclobutene' description, suggesting that, at most, only partial oxidative addition of the B-C bond has occurred. The angles at the non-metal-bound carbon atom of known Pt II metallacyclobutenes (100°, 101° and 104.7(7)°) [41][42][43] are diagnostic for a 'complete addition' description, while the analogous angle in 2 (80.7(5)°) suggests that the BC 2 ring is significantly more intact.…”

“…Sakaki predicts B-C distances of 2.336-2.611 Å (149-166% of the sum of the covalent radii, Σ covrad ) in B-C bond oxidative addition products cis-[(R 3 P) 2 Pt{B(OH) 2 }(CH 3 )] (R 3 = H 3 , H 2 Me, H 2 Et). Figure 2 shows that analogous distances in metallacyclobutene derivatives in which BR is replaced with CR 2 , NR or O (145-169% of Σ covrad ) are all significantly longer than that of 2 (121% of Σ covrad )-this includes highly comparable platinacyclobutene structures [41][42][43] . The Pt-C distance in 2 is within the range found in classical σ-vinyl complexes, whereas the Pt-B distance is slightly longer than those found in Pt-boryl complexes, although a part of this lengthening could stem from the bulky mesityl group at boron 53 .…”

“…Isolated reports of oxidative addition of B-C bonds to transition metals exist 39,40 , making activation of this bond an intriguing target. Facile oxidative addition of cyclic C-C single bonds to Pt 0 has been documented with cyclopropenones 41 , methylenecyclopropenes 42 and tetrafluorocyclopropene 43 (Fig. 1b), while examples of B-B oxidative addition are numerous 44 .…”

Ruthenium-catalyzed insertion of adjacent diol carbon atoms into C-C bonds: Entry to type II polyketides

“…For example, Halpern described the reaction of cubane and quadricyclane, respectively, with [Rh(CO) 2 Cl] 2 to form rhodacycles (5, 6). The oxidative additions of a platinum(0) complex to diphenylcyclopropenone and benzocyclobutene dione, respectively, to form 4- and 5-membered platinacycles were documented soon thereafter (7, 8). The utility of metallacycles obtained through C-C bond oxidative addition vis-à-vis π-bond insertion was demonstrated in stoichiometric alkyne-cyclobutene cycloadditions by Liebeskind (9, 10), who later showed such reactions can be catalyzed by nickel(0) (11).…”