Platinum−Molybdenum Complexes of Cyclic Tropynes, Cumulenes, and Alkynes

Abstract

The bis(triphenylphosphine)platinum complexes of tropyne (1), cyclohepta-3,5-dien-1-yne (12), and cyclohepta-1,5-dien-3-yne (13) react rapidly with (η6-p-xylene)Mo(CO)3 in a mixture of CD2Cl2 and THF-d 8 to give the bimetallic complexes 4−6. Reduction of 4 with LiAl(O-t-Bu)3H or KBEt3H gives a mixture of 5−7 (essentially quantitative) in a ratio of 5:10:85 and 8:21:71, respectively. The major isomer contains a 1,2,3,5-cycloheptatetraene ring, a ring system that has previously been inaccessible either free or complexed to a transition metal. Hydride abstraction from 5, 6, or 7 regenerates 4. X-ray crystal structures for 5 and 7 are reported. The absolute configuration of complex 7 in the crystal was determined.

Twists and Turns of Platinum-Allene Complexes: NMR Techniques for the Study of the Dynamic Behavior in Solution

“…Some data have been already reported in the study of fluxional behavior in Pt­(II)- and Pt(0)-allene complexes using line-shape analysis and SST NMR techniques. The helical movement or 1,2-metal shift has been studied in Pt-cyclic allene complexes (where the rotational movement is not possible due to the rigidity of the system) by Jones et al using magnetization transfer experiments . They showed that a cationic Pt­(II)-cyclo­hepta­trienyli­dene complex exists preferably as the η 1 -carbene tropylium ion form in solution, or as a very fast equilibrium between the η 2 -Pt-allene structures (Scheme ).…”

Bis(triphenylphosphine)palladium Cycloheptadienynylium Tetrafluoroborate: A Palladium Complex of Tropyne

“…Transition metal complexes containing six-membered arynes in their coordination sphere have generated considerable interest in recent years due to their rich chemistry and unique structural features . We have been interested for some time in complexes containing seven-membered ring arynes as ligands which led to the preparation of a platinum tropyne complex 1 , its dibenzannelated analogue, a zirconium tropyne complex 2 , and a Pt−Mo bimetallic tropyne complex 3 …”

Generation and Reactions of a Benzodehydrotropylium Ion–Co2(CO)6 Complex

“…9 The η 2 -platinum(0), palladium(0), and zirconium(II) complexes of a dehydrotropylium ion or related cations have been prepared by the Jones group and show no to modest C–C bond alternation. 7 Dehydrotropone–Co 2 (CO) 4 (dppm) shows considerable bond alternation. 10…”

“…The development of the aforementioned multiple cycloheptynedicobalt preparation methods has allowed our group to make contributions to the study of metal complexes of the putatively aromatic 1,2-dehydrotropylium ion (henceforth referred to simply as a dehydrotropylium ion). We have reported the generation, trapping, and evaluation of a dehydrotropylium ion −Co 2 (CO) 6 complex ( 2 ) and found a reduced level of aromatic stabilization in that system, approximately 25% of that of a tropylium ion, employing NICS(1) calculations and homodesmotic reactions as the primary measures. , By contrast, a dehydrotropylium ion itself only has been proposed as a mass spectral fragment of 2-acylbenzofurans and benzothiophene, and neither has it been prepared synthetically nor has had its properties investigated . The η 2 -platinum­(0), palladium(0), and zirconium­(II) complexes of a dehydrotropylium ion or related cations have been prepared by the Jones group and show no to modest C–C bond alternation .…”