Niobium-mediated synthesis of phosphorus-rich molecules

The use of a sterically demanding enolate ligand -OC[2Ad]Mes supported by niobium has allowed for the synthesis of (Mes[2Ad]CO) 3Nb=PP7Nb(OC [2Ad]Mes)3 through P4 coupling by a low-valent niobium intermediate. This asymmetric phosphorus-rich cluster harbors a niobium phosphinidene unit bound to a niobium-supported P7 cluster. The phosphinidene terminus was found to react with a range of ketones to give phosphaalkene complexes R2C=PP7Nb(OC[2Ad]Mes) 3. These phosphaalkenes are unstable towards intramolecular rearrangement to give R2CP8Nb(OC[ 2Ad]Mes)3 in which the carbene unit has been internalized into the P8 cage. This rearrangement was studied through both Eyring and Hammett analyses. Structrually the new R2CPsNb(OC[2Ad]Mes)3 are viewed as coordinated-diphosphenes and it was found that the diphosphene unit could be liberated and trapped by reaction with pyridine-N-oxide in the presence of excess 1,3-cyclohexadiene, generating niobium oxo and R2CP8(C 6H8). Searching for new platforms to investigate niobium-phosphorus chemistry led to the synthesis of [Na(THF) 3][P3Nb(ODipp) 3], an anionic cyclo-P3 complex that is accessible in two steps from commercially available reagents. It was discovered that [Na(THF) 3] [P3Nb(ODipp) 3] could function as a source of P3 3-, which has allowed for the synthesis of the tetraatomic molecule AsP 3 as a pure substance for the first time. AsP 3 has been studied by gas-phase electron diffraction, photoelectron spectroscopy, solid-state NMR spectroscopy, raman spectroscopy, as well as high resolution mass spectrometry, and a variety of quantum chemical calculations. Further, a wide array of AsP3 reaction chemistry has been probed including the synthesis and structural characterization of two metal complexes with a coordinated, intact AsP3 ligand. Motivated to explore the chemistry of [Na(THF)3][P3Nb(ODipp) 3] further, a series of investigations were carried out to generate substituted triphosphirene ligands complexed to niobium. In particular Ph3SnP3Nb(ODipp) 3 was prepared and was found to react cleanly and efficiently with pyridine-N-oxide in the presence of an excess of 1,3-cyclohexadiene to generate the niobium oxo complex and Ph3SnP3(C6H8), the product of a Diels-Alder reaction between the liberated triphosphirene and 1,3-cyclohexadiene. This unusual phosphorus-rich molecule was exploited in a number of transformations. One reaction of particular interest was the synthesis of P3Rh(PPh 3)3 from Ph3SnP3(C6Hg) and Wilkinson's catalyst (ClRh(PPh3)3) with loss of 1,3-cyclohexadiene and ClSnPh3- This transformation is an illustrative example of the ability of Ph3SnP 3(C6H8) to act as a P3 transfer agent.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Chemistry.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2010

Author dc:creator

• Cossairt, Brandi M. (Brandi Michelle)

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/1721.1/57702

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/57702