Reaction of (.eta.5-C5Ph5)2Mo2(CO)6 with a chelating phosphine ligand: generation of stable 17- and 19-electron complexes. Dynamic equilibrium of (.eta.5-C5Ph5)2Mo2(CO)6 and (.eta.5-C5Ph5)Mo(CO)3

Abstract

The synthesis of the (7)5-C6Ph5)2Mo2(CO)6 complex is described. In solution, the dimer is in equilibrium with 2 17-electron (jj5-C5Ph5)Mo(CO)3 monomers.The equilibrium constant for the dimer-monomer equilibrium, as determined by electronic absorption spectroscopy, is 8.7 (±5.1) X 10™5 at 23 °C. (A 1 X 10"4 M solution of the dimer is thus 40% ± 15% dissociated.) (775-C5Ph6)2Mo2(CO)6 reacts with L2 (L2 is the chelating phosphine ligand 2,3-bis(diphenylphosphino)maleic anhydride) to form the 19-electron ("18 + 5") (7j5-C5Ph5)Mo(CO)2(L2-P,P/) and the 17-electron (Tj5-CgPhs)Mo(CO)2(L2-P) complexes. (L2-P,P' indicates two P atoms are coordinated, and L2-P indicates one P atom is coordinated.) Variable-temperature electron spin resonance (ESR) showed a dynamic equilibrium between these 19-and 17-electron complexes with lower temperature favoring the 19-electron complex, and higher temperature the 17-electron complex. The (7)5-C5Ph5)Mo(CO)2(L2-P,P') complex has two magnetically equivalent P atoms, and the room-temperature ESR spectrum is a 1:2:1 triplet. This spectrum and its temperature-dependent behavior is compared and contrasted with the spectrum of the analogous ()?5-C5Ph4H)Mo(CO)2(L2-P,P') complex. Infrared, ESR, and electronic spectroscopic data are reported for all of the complexes generated in this study.

Organometallic Radicals: Thermodynamics, Kinetics, and Reaction Mechanisms

“…An exception is the report by Tyler and coworkers 44 of an equilibrium generating the . For the Mo and W complexes, due to their stronger M--M bonds, there is no sign of significant radical concentrations present in solution at room temperature for .…”

Investigation of organometallic reaction mechanisms with one and two dimensional vibrational spectroscopy

“…The organometallic species and solvent were the same in all experiments conducted, so differences in chemical dynamics result solely from the different properties of the three coordinating ligands (PR 3 ; R = OMe, Bu, Ph). A low energy π* orbital in the coordinating ligand tends to enhance the stability of 18+δ compounds since the '19th' electron can localize in the anti-bonding orbital rather than occupying a higher energy metal-centered orbital [127][128][129]. Reduction potentials of the lone ligand are correlated with the ligand's ability to stabilize 18+δ compounds by accommodating the extra electron in a vacant molecular orbital [129,164,165].…”

“…In addition to electron deficient 17-electron (17e) radicals, 19-electron (19e) species have been identified as potential intermediates in a variety of catalytic and electron transfer reactions [122][123][124]. One of the first 19e complexes, cobaltocene, was synthesized as early as 1953 [125,126], and many stable 19e complexes have subsequently been characterized [127][128][129][130]. While these complexes formally contain 19 valence electrons, the '19th' electron is commonly localized on a ligand, allowing the metal to retain an effective 18-electron count.…”

“…For example, the first 19e complex, cobaltocene, was isolated more than fifty years ago [125,126] and a variety of similar complexes have since been identified [127][128][129][130]. The descriptor "19-electron" comes with some qualification-the '19th' or unpaired electron is usually localized on a ligand rather than the transition-metal atom [129,130].…”

[Me2C(η5-C5H4)2Ru2(CO)4]—An Organometallic Thermo-Optical Switch

“…In general, photochemically generated metal‐centered radicals, [CpM . (CO) n ], are extremely short‐lived transients and recombine with nearly diffusion controlled rates 20–22, 27, 28. Hence, only sufficiently fast atom‐abstraction reactions from suitable organic substrates (mostly organic halides) can compete with the radical recombination process 19, 22, 27.…”