Bond Formation Reactions to Phosphorus Using an Electrophilic Phosphinidene Complex

Vaheesar, Kandasamy
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Faculty of Graduate Studies and Research, University of Regina

Electrophilic phosphinidene complexes play a central role in organophosphorus chemistry. The chemistry of transient phosphinidene complexes has been well studied, but stable, cationic phosphinidene complexes are not as well understood. Therefore the reactivity of a cationic phosphinidene complex [CpFe(CO)2{PNiPr2}]+ (Cp = η5-cyclopentadienyl, iPr = isopropyl), toward bond activation, cycloaddition and nucleophilic addition has been examined. The complex [CpFe(CO)2{PNiPr2}]+ reacts with primary, secondary, and tertiary silanes to form the silyl phosphine complexes [CpFe(CO)2{P(H)(SiR3)NiPr2}]+ (SiR3 = SiPhH2, SiPh2H, Si(C2H5)3), in which the phosphinidene has inserted into the Si-H bond. A computational study shows that the insertion is concerted. The same phosphinidene complex reacts with HPPh2 to form the phosphine-coordinated phosphinidene complex [CpFe(CO)2{P(PHPh2)NiPr2}]+, which rearranges to the phosphino-phosphine complex [CpFe(CO)2{P(PPh2)(H)NiPr2}]+. Reaction of [CpFe(CO)2{PNiPr2}]+ with H2 at high pressure leads to the primary phosphine complex [CpFe(CO)2{PH2(NiPr2)}]+. The phosphinidene complex [CpFe(CO)2{PNiPr2}]+ reacts with alkenes and alkynes via (1+2) cycloaddition to form phosphiranes and phosphirenes respectively. Conjugated alkenes react to initially form phosphiranes, which rearrange to phospholenes via a [1+3] sigmatropic shift. Reaction with an α, β unsaturated ketone gives an oxo-3-phospholene complex. Reaction with azobenzene forms a benzodiazophosphole via C-H activation. Addition of HCl or HBF4·O(CH3CH2)2 to the phosphirene and benzodiazophosphole complexes results in P-N bond cleavage, yielding the respective chlorophosphorus heterocyclic complexes. The heterocycles can be removed from the metal complexes by addition of trimethylphosphine or triethylphosphine. The phosphinidene complex [CpFe(CO)2{PNiPr2}]+, reacts with trialkylphos-phines to form the phosphine-coordinated phosphinidene complexes [CpFe(CO)2-{P(PR3)NiPr2]+ (R = CH3, C2H5, C4H9). Phosphines act as a protecting group and allow amine cleavage via reaction with HBF4·O(CH3CH2)2 to form phosphine-coordinated chlorophosphinidene complexes. The resulting chloro group can be displaced by an additional phosphine, leading to novel bisphosphoniophosphido complexes [CpFe(CO)2{P(PR3)}]2+, which rapidly dissociates to form [PR3-P-PR3]+. Reaction of [CpFe(CO)2{PNiPr2}]+ with bis(dimethylphosphino)methane forms [CpFe(CO)-{P(NiPr2)P(Me2)CH2P(Me2)-κ2P1,P4}]+. P-N cleavage of the bridging complex [CpFe(CO){P(NiPr2)P(Me2)CH2P(Me2)-κ2P1,P4}]+ with HCl leads to [CpFe(CO)-{P(Cl)P(Me2)CH2P(Me2)-κ2P1,P4}]+. Phosphine addition to [CpFe(CO){P(Cl)-P(Me2)CH2P(Me2)-κ2P1,P4}]+ gives the bisphosphoniophosphido complex [CpFe(CO)-{P(PR3)P(Me2)CH2P(Me2)-κ2P1,P4}]2+, which is stable to dissociation. The reactivity studies of [CpFe(CO)2{PNiPr2}]+ have shown that it can be used to activate non-polar bonds like Si-H, P-H and H-H to form P-Si, P-P and P-H bonds, but is not electrophilic enough to activate C-H bonds. [CpFe(CO)2{PNiPr2}]+ undergoes cycloaddition reactions with a wide range of unsaturated substrates leading to phosphorus heterocycles, and shows the typical reactivity expected for electrophilic phosphinidene complexes. Novel complexes with P-P-P ligands and P-P bonds have been formed via phosphine addition reactions of [CpFe(CO)2{PNiPr2}]+.

A Thesis Submitted to the Faculty of Graduate Studies and Research In Partial Fulfillment of the Requirements For the Degree of Doctor of Philosophy in Chemistry, University of Regina. xiv, 179 p.