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Thermochemical Studies of Ni(II) and Zn(II) Ternary Complexes Using Ion Mobility-Mass Spectrometry
Published on: June 8, 2022
Neutral and zwitterionic low-coordinate titanium complexes bearing the terminal phosphinidene functionality.
Guangyu Zhao1, Falguni Basuli, Uriah J Kilgore
1Department of Chemistry and Molecular Structure Center, Indiana University, Bloomington, IN 47405, USA.
Abstract:
Alpha-hydrogen abstraction and alpha-hydrogen migration reactions yield novel titanium(IV) complexes bearing terminal phosphinidene ligands. Via an alpha-H migration reaction, the phosphinidene ((tBu)nacnac)Ti=P[Trip](CH(2)(tBu) ((tBu)nacnac(-) = [Ar]NC((t)Bu)CHC((t)Bu)N[Ar], Ar = 2,6-(CHMe2)(2C6H3, Trip = 2,4,6-(i)Pr3C6H2) was prepared by the addition of the primary phosphide LiPH[Trip] to the nucleophilic alkylidene triflato complex ((tBu)nacnac)Ti=CH(t)Bu(OTf), while alpha-H abstraction was promoted by the addition of LiPH[Trip] to the dimethyl triflato precursor ((tBu)nacnac)Ti(CH)(2)(OTf) to afford ((tBu)nacnac)Ti=P[Trip](CH3). Treatment of ((tBu)nacnac)Ti=P[Trip](CH3) with B(C6F5)(3) induces methide abstraction concurrent with formation of the first titanium(IV) phosphinidene zwitterion complex ((tBu)nacnac)Ti=P[Trip]{CH3B(C6F5)(3)}. Complex ((tBu)nacnac)Ti=P[Trip]{CH3B(C6F5)(3)} [2 + 2] cycloadds readily PhCCPh to afford the phosphametallacyclobutene [((tBu)nacnac)Ti(P[Trip]PhCCPh)][CH3B(C6F5)(3)]. These titanium(IV) phosphinidene complexes possess the shortest Ti=P bonds reported, have linear phosphinidene groups, and reveal significantly upfielded solution 31P NMR spectroscopic resonances for the phosphinidene phosphorus. Solid state 31P NMR spectroscopic data also corroborate with all three complexes possessing considerably shielded chemical shifts for the linear and terminal phosphinidene functionality. In addition, high-level DFT studies on the phosphinidenes suggest the terminal phosphinidene linkage to be stabilized via a pseudo Ti[triple bond]P bond. Linearity about the Ti-P-C(ipso) linkage is highly dependent on the sterically encumbering substituents protecting the phosphinidene. Complex ((tBu)nacnac)Ti=P[Trip]{CH3B(C6F5))(3)} can catalyze the hydrophosphination of PhCCPh with H(2)PPh to produce the secondary vinylphosphine HP[Ph]PhC=CHPh. In addition, we demonstrate that this zwitterion is a powerful phospha-Staudinger reagent and can therefore act as a carboamination precatalyst of diphenylacetylene with aldimines.
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