Two-electron mixed-valence complexes small molecule activation and photocatalytic hydrogen production

Two-electron mixed-valence complexes of rhodium may be supported by diphosphazane ligands (RN(PY2)2). Whereas diphosphazane ligands with strongly [pi]-acidic phosphine groups (Y = F, OCH2CF3) react with RhI starting materials to afford binuclear Rh20,II complexes, Rh20,II(MeN(PY)2)3X2(L) or Rh2"II(MeN(PY),)3X2 (X = Cl, Br), diphosphazane ligands with weaker [pi]-acid phosphines (Y = OMe, OPh) give only valence-symmetric Rh2I,I complexes, Rh2I,I(MeN(PY2)2X2(L)2. Moreover, the formation of Rh20,II(tfepma)3C12 and [ClRh'(tfepx)]2([mu]-tfepx) (tfepma = MeN[P(OCH2CF3)2]2; tfepx = (3,5-Me2C6H3)N[P(OCH2CF3)2] suggest that delocalization of the nitrogen lone pair into the [pi]-system of the aryl group defeats formation of the two-electron mixed-valence species. These results are interpreted in terms of a polarizable nitrogen lone pair mediating the [pi]-acid properties of the PY2 groups to induce disproportionation of valence-symmetric dirhodium cores. Application of this knowledge to iridium provided the first example of a two-electron mixed-valence complex for this metal, Ir20,II(tfepma)3C12. X-ray diffraction studies reveal a coordination environment with two bridging tfepma ligands and a third tfepma chelating the Ir0 center. Trigonal bipyramidal geometry at the Ir0 is completed by a metal-metal bond to a square pyramidal IrII containing cis-disposed chloride ligands. Ir20-II(tfepma)3C12 is Lewis-acidic, readily accepting donor ligands to form 36 e- complexes. Oxidative addition is also rapid: chlorine and hydrogen chloride react to afford Ir2I-III(tfepma)3C14 and Ir2I,III(tfepma)3HC13, respectively. Hydrogen adds reversibly to Ir20,II(tfepma)3C12, providing the first example of such an addition across a preserved metal-metal single bond.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Chemistry.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2001

Author dc:creator

• Heyduk, Alan F. (Alan Frank), 1974-

Advisor dc:contributor.advisor

• Daniel G. Nocera.

• 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/1721.1/8251

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/8251