You are here

Home » SYNTHESIS, CHARACTERIZATIONS AND REACTIONS OF LOW VALENT COMPLEXES OF MOLYBDENUM CONTAINING [BIS(2-DIPHENYLPHOSPHINOETHYL) PHENYL-PHOSPHINE] AND A NITROGEN FIXATION APPROACH

SYNTHESIS, CHARACTERIZATIONS AND REACTIONS OF LOW VALENT COMPLEXES OF MOLYBDENUM CONTAINING [BIS(2-DIPHENYLPHOSPHINOETHYL) PHENYL-PHOSPHINE] AND A NITROGEN FIXATION APPROACH

Primary tabs

Hassan H. HAMMUD

 

Univ.

University of Nebraska

Spec.

Chemistry

Dip.

Year

# Pages

Ph.D.

1994

153

 

 High energy electron rich molybdenum phosphine complexes were synthesised by the reduction of [Mo(TRI)C13] in THF with sodium amalgam in the presence of various ligands: arenes, cyclopentadiene, indene, dinitrogen, phosphines and phosphites; (TRI is [Bis(2 ­diphenylphosphinoethyl)phenylphosphine]. The products are: i, [Mo(,η6 ‑arene) (TRI)], (arene = C6H6, C6H5OCH3, C6H5CH3, C10H8 or PPh3); ii, [Mo(η5‑C5H5)(TRI)H]; iii, [Mo(η5‑C9H7)(TRI)H];iv,fac- [Mo(N2)(TRI)(PMe3) 2]; v, [Mo(N2)( η3‑TRI)( η 2‑TRI)]; vi, mer-­[Mo(TRI)(P(OR)3)3], (R = Me or Et). When THF solvent was used and in the abscence of added ligands, the products are [Mo(TRI)(THF)3] under argon and { Mo(N2) (TRI) (THF3) }x under dinitrogen.

 Heating fac‑[Mo(N2)(TRI)(PPhMe2)2] in THF with ethylene produced trans‑[Mo(CH2 CH2) 2(TRI) (PPhMe2. Heating trans­- [Mo(N2)2(TRI)(PPh3 in THF formed [Mo(η6‑PhPPh2 (TRI)] by rearrangement of σ- to η6‑bonded PPh3. Reaction of [Mo(η6-­arene)(TRI)] with strong acid formed [Mo(η6‑C6H6)(TRI)H]+ and [Mo(η6‑arene)(TRI)(H)2]2+.

The hydride complex [Mo(η5‑C5H5)(TRI)H] was also prepared by heating fac‑[Mo(N2)(TRI)(PMe3)2] with cyclopentadiene in heptane. The hydride complex reacted with CDC13 forming [Mo(η5‑C5H5) ‑(TRI)C1] and [Mo(η5‑C5H5)(TRI)(CC13)l (Mass spectra: m+l/z = 732 and 818 respectively).

Mer‑[Mo(TRI)(P(OR)3)3] isomerizes to fac‑[Mo(TRI)(P(OR)3)3] both thermally and photochemically.

Both Mer-[Mo(TRI)(P(OR)3)3] and [Mo(η6‑arene)(TRI)] exhibit two oxidation waves in the cyclic voltammograms in THF. The first oxidation is reversible but the second oxidation is pseudoreversible.

The reaction of HBr with trans‑[Mo(N2)2(dppe)(PPh2Me)2] in THF formed  [Mo(NNH2) (THF) (dppe) (PPh2Me)Br]Br, [Mo(NNH2)(dppe)-­(PPh2Me)2 Br]Br and [Mo(NNH2)     (dppe)(PPh2Me)Br2]. The reaction of [Mo(NNH2) (dppe) (PPh2Me) (Br)2]with pyridine formed the diamagnetic [Mo(NNH2)(dppe)(PPh2Me)(C5H5N)Br]Br. In contrast, the reactions of [Mo(NNH2)(dppe)(PPh2Me)Br2] or [Mo(NNH2)(dppe)-­(PPh2Me)2Br]Br with pyrazine formed the purple paramagnetic [Mo(NNH2)(dppe)(PPh2Me)(C4H4N2)Br]Br, (UV, λ = 572 nm). A mechanism for ammonia and hydrazine production was proposed. It involves a series of electronation and protonation steps.

Finally, the reactions of fac‑[Mo(N2)(TRI)(PMe3)2] and fac- [Mo(N2) (TRI) (dppm) ]       produced the corresponding carbon dioxide complexes, IR (KBr), v(C02) = 1758.80 and 1779.98 cm‑1 respectively.