Synthons for carbide complex chemistry

Abstract

The sterically accessible carbide complex, (Cy3P)Cl3Ru[triple bond, length as m-dash]C-PtCl(py)2, acts as a synthon for terminal and bridging carbide fragments that relocate to pincer and A-frame scaffolds upon ligand addition. This concept, benefitting from coordination sphere selection as the concluding step, confronts traditional synthetic strategies and broadens the scope for carbide complexes.

Chromium carbides and cyclopropenylidenes

“…The 5coordinate chromium center is best described as distorted Please do not adjust margins Please do not adjust margins square pyramidal ( 5 = 0.29) 59 with the carbido ligand on the apical position along with a short Cr1-C1 bond (1.634(10) Å), while the other chromium center represents a distorted octahedral geometry with a long Cr2-C1 bond (2.035(10) Å). Akin to the reported mononuclear neutral carbides and dinuclear dative bonding carbides, two X-type ligands (halides) and two L-type ligands (THF, pyridine, PR 3 or NHC) are transoid each other on the basal positions in the 5-coordinate environment, but the  5 values of 4-thf ( 5 = 0.41) and 4-py ( 5 = 0.29) are larger than those of the mononuclear neutral carbides ( 5 = 0.07-0.16) [17][18][19][20] and dinuclear dative bonding carbides ( 5 = 0.01-0.23) [21][22][23][24][25] of ruthenium and osmium. Given the S = 2 nature of 4-thf in THF by Evans' method ( eff = 4.84 60 as well as in solid-state ( eff = 5.03), 55 the Wiberg bond indices of Cr1-C1 and Cr2-C1 bonds were calculated as 2.02 and 1.08, respectively, for 4-thf and 2.07 and 1.12 for 4-py.…”

“…2c). Therefore, the canonical structure of the carbido complex 4 could be better described as a dative bonding -carbide [21][22][23][24][25] than the metallocarbyne character. [27][28][29][30][31] Scheme 3 Reduction of C-Br bonds with CrBr 2 and formation of 4-thf (Cr = CrBr 2 (thf) n ).…”

“…The neutral carbido complexes [(L) 2 Cl 2 M≡C:] (M = Ru, [17][18][19] Os; 20 L = PPh 3 , PCy 3 , NHC), originally synthesized by Heppert in 2002, 17 can form dative bonding Lewis pairs with various transition metals. [21][22][23][24][25] The anionic terminal carbide [(Ar t BuN) 3 Mo≡C] -(Ar = m-Xylyl) has been prepared by Cummins and coworkers via deprotonation of a terminal methylidyne complex. 26 Akin to the neutral terminal carbides, [17][18][19][20][21] the anionic carbides also bind various metals to form dinuclear structures, but those dinuclear carbido complexes have a metallocarbyne character.…”

Transition Metal Carbide Complexes

“…The bimetallic carbide complex reacts with two equivalents of the pincer ligand, Ad PNP, to generate [Pt­( Ad PNP)­Cl]Cl and [( Ad PNP)­ClRuC]­Cl. Similarly, [(Cy 3 P)­Cl 3 RuC–PtCl­(py) 2 ] reacts with PPh 3 to generate cis -[PtCl 2 (PPh 3 ) 2 ] and unstable [(Ph 3 P)­(Cy 3 P)­Cl 2 RuC] . The mixed PCy 3 /PPh 3 carbide complex slowly decays, leaving [(Cy 3 P) 2 Cl 2 RuC] as the only carbide product, and in this context, it is noteworthy that the hypothetical carbide complex, “[(Ph 3 P) 2 Cl 2 RuC]”, fails to form via elimination of dimethyl fumarate from [(Ph 3 P) 2 Cl 2 RuC­{CHCO 2 Me} 2 ] (Figure ).…”

“…Surprisingly, conversion of [(Cy 3 P) 2 Cl 2 RuC] with trans -[PtCl 2 (py) 2 ] consumes two equivalents of the Pt II complex, affording [(Cy 3 P)­Cl 3 RuC–PtCl­(py) 2 ] along with the salt, trans -[PtCl­(py) 2 (PCy 3 )]Cl (Figure ). The carbide-bridged monophosphine complex reacts readily with the diphosphine, dppm, to afford the A-frame-like complex, [(μ-dppm) 2 Cl 3 RuC–PtCl]. The more sterically congested diphosphine, dcpm, reacts sluggishly, producing a persistent {(μ-dcpm)­(Cy 3 P)­RuC–Pt} intermediate (identified by 31 P NMR spectroscopy).…”