Niobium-mediated generation of P-P multiply bonded intermediates

The diphosphaazide complex (MesNPP)Nb(N[CH2 tBu]Ar)3, 1 (Mes = 2,4,6-tri-tert-butylphenyl, Ar = 3,5-dimethylphenyl), releases a P2 unit upon heating to form MesNNb(N[CH2 tBu]Ar)3, 2, in a first-order process. The chemistry of the putative P2 intermediate was probed with a variety of reagents. It was successfully transferred to organic dienes to yield polycyclic diphosphines, and also to terminal phosphide complexes of the general formula P????M(N[R]Ar)3 to yield cyclo-P3 complexes. Coordination of W(CO)5 to 1 accelerates conversion to 2, with loss of the (P2)W(CO)5 fragment, such that this reaction occurs readily at 20 C. The (P2)W(CO)5 fragment was transferred to the same substrates listed above, as well as to a low-valent platinum source. In all cases, this transfer occurs in higher yields than for the uncomplexed P2. Kinetic measurements on the elimination reactions showed them to be first-order in diphosphaazide complex and independent of substrate concentration, consistent with the hypothesis that P2 and (P2)W(CO)5 are released into solution as discrete species. The above reaction chemistry was used to synthesize reactive, anionic cyclo-P3 complexes of niobium with formulas [f(OC)5Wgn(P3)Nb(N[CH2 tBu] Ar)3]- (n = 0;1; 2). These complexes were shown to react with the electrophiles Ph3SnCl, MesNPCl, and RC(O)Cl to yield coordinated h2-triphosphirene complexes. The acyltriphosphirene complexes [(OC)5W]2RC(O)P3Nb(N[CH2-tBu]Ar)3 are unstable toward loss of an RCP3[W(CO)5]2 fragment and formation of oxoniobium ONb(N[CH2 tBu]Ar)3.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Chemistry.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2009

Author dc:creator

• Piro, Nicholas A. (Nicholas Anthony)

Advisor dc:contributor.advisor

• Christopher C. Cummins.

• Chemistry.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/49552

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/49552