Investigation of phosphine containing ligands including tridentate diphosphine diazaphospholeniums and their transition metal complexes

Historically, the coordination of N-heterocyclic phosphenium/phosphido (NHP+/NHP-) ligands incorporated into a chelating diphosphine ligand framework (PPP) to late transition metals has revealed a variety of possible binding modes. In continuation of previous work, PPP-nickel coordination compounds and new diphosphine/NHP+ compounds have been synthesized and investigated. Treatment of the chlorophosphine precursor (PPP)Cl with a stoichiometric amount Ni(COD)2 led to the formation (PPP)NiCl which has been described as an NHP-/NiII complex. The NHP--bridged NiII/Ni0/Ni II compound (PPP)2Ni3Cl2, and the reduced NiINiI dimer [(PPP)Ni]2 were synthesized using excess Ni(COD)2 and the (PPP)Cl ligand. An asymmetrically-bridged dication [(PPP)Ni]2[PF6]2, in which two Ni 0 centers are bridged by two NHP+ cations, was synthesized when [PPP][PF6] was used as the ligand precursor. Comproportionation of the reduced, neutral [(PPP)Ni]2 dimer and the dicationic [(PPP)Ni] 2[PF6]2 complex afforded the mixed-valent monocationic dimer [(PPP)Ni]2[PF6]. Examination of the crystal structures as well as density functional theory calculations have been used to assess the electronic structure and bonding in the mono-, bimetallic compounds, and highlight the redox non-innocence of NHP+/- ligands.;The coordination of a Cp- anion to the PPP ligand via the addition of LiCp to the (PPP)Cl precursor resulted in the formation of two eta1 [PPP]Cp compounds including both the vinylic and allylic NHP-Cp isomers, as well as the deprotonated compound [PPP(C5 H4)][Li]. The vinylic PPP(C5H5) compound, in which the eta1 Cp has undergone a [1,5]-hydride shift, was the major product. Using excess LiCp as a base, PPP(C5H 4) can be synthesized independently. Treatment of (PPP)Cl with two equivalents of NiCp2 resulted in the formation of [(micro-PPP)Ni2Cp 2]Cl, which has been described as a NiIINiII system bridged by one NHP- ligand. The addition of PPh 3 to a reaction of (PPP)Cl and NiCp2 was shown to facilitate the migration of a Cp ring from the metal to the PNHP of the ligand resulting in the formation of (PP(C5H5)P)NiCl 2. Again, the C5H5 ring was found to be the vinylic isomer bound to the PNHP in an eta1 fashion. Deprotonation of (PP(C5H5)P)NiCl2 resulted in the formation of the zwitterionic complex (PP(C5H4)P)NiCl. Calculations were used to assess the electronic structure and bonding of the [(microPPP)(NiCp)2]+, (PP(C5H 5)P)NiCl2, and (PP(C5H4)P)NiCl complexes.;Two new tridentate diphosphine NHP-Cl ligands have been synthesized varying the aromaticity and size of the heterocycle. A tridentate diphosphine NHP-Cl with a ring-fused aromatic phenylene backbone was synthesized (ArPPP)Cl. Additionally, a ring-expanded 6-membered NHP-Cl with pendent phosphine side arms, cyclohexyl(PPP)Cl, was synthesized along with the cationic cyclohexyl[(PPP)][PF6] ligand. Preliminary results in the coordination of (cyclohexylPPP)Cl to NaCo(CO) 4 and PdCp(allyl) suggests the formation of kappa2-cyclohexyl(PPP)Co(CO) 3, tentatively assigned as NHP-/CoI with only one bound phosphine side arm, and cyclohexyl(PPP)Pd-Cl, tentatively assigned as NHP-/PdII.;Finally, heterobimetallic complexes featuring three bidentate phosphinoamide ligands bridging a CoI center and a Nb or Ta imido fragment have been synthesized. The resulting heterobimetallic complexes, ICo(Ph 2PNiPr)3M=N tBu, are shown to have weakened dative metal-metal interactions as a result of the strongly donating imido ligand, in comparison to similar, previously reported compounds. The ICo(Ph2PNiPr) 3M=NtBu complexes can be reduced by two electrons to generate dinitrogen-bound complexes.