title: Sterically-constrained tripodal phosphorus-bridged tris-pyridyl ligands.
abstract: Introducing substituents into the 6-position of the 2-pyridyl rings of neutral tris-pyridyl phosphanes of the type P(2-py')3 (where 2-py' is a substituted 2-pyridyl ring), has a marked impact on their coordination of transition metal ions, as revealed in the current study. Whereas the unsubstituted phosphorus-bridged tris-pyridyl ligand P(2-py)3 (1) forms the sandwich cation [{P(py)3}2Fe](2+) (4) with iron(II), coordinating via all of the donor nitrogen atoms, the reaction of the methyl-substituted counterpart P(6-Me-2-py)3 (2) and FeCl2 results in the half-sandwich arrangement [{P(6-Me-2-py)3}FeCl2]·toluene (5·toluene), in which only two N-atoms of the ligand coordinate to the metal. A similar half-sandwich type complex, [{P(6-Me-2-py)3}FeCl(OTf)]·2THF (6·2THF), is obtained from reaction of 2 with Fe(OTf)2 in the presence of LiCl, only now with all three of the N-atoms of the ligand coordinated to Fe(II). The formation of a half-rather than full-sandwich complex 2 with suggests that steric clashing of the Me groups prevents the formation of sandwich-type arrangements. The reaction of [Cu(MeCN)4]PF6 with P(6-Me-2-py) (2) gives the complex [(MeCN)3Cu{P(6-Me-2-py)3}Cu(MeCN)](PF6)2 (7), in which two Cu(I) atoms are coordinated by the bridgehead P-atom and by the three N-atoms of the tris-pyridyl ligand (a unique coordination mode in this area). Overall, the results indicate that 6-Me substitution results in a promising 6-electron capping ligand for organometallic synthesis and catalysis.
authors.affiliation: Chemistry Department, Cambridge University, Lensfield Road, CB2 1EW, Cambridge, UK. dsw1000@cam.ac.uk.
authors.forename: Schirin
authors.initials: S
authors.lastname: Hanf
authors.affiliation: Chemistry Department, Cambridge University, Lensfield Road, CB2 1EW, Cambridge, UK. dsw1000@cam.ac.uk.
authors.forename: Raúl
authors.initials: R
authors.lastname: García-Rodríguez
authors.affiliation: Chemistry Department, Cambridge University, Lensfield Road, CB2 1EW, Cambridge, UK. dsw1000@cam.ac.uk.
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Bond
authors.affiliation: Institute of Inorganic Chemistry, Faculty of Chemistry and Mineralogy, Leipzig University, Johannisallee 29, 04103 Leipzig, Germany. hey@uni-leipzig.de.
authors.forename: Evamarie
authors.initials: E
authors.lastname: Hey-Hawkins
authors.affiliation: Chemistry Department, Cambridge University, Lensfield Road, CB2 1EW, Cambridge, UK. dsw1000@cam.ac.uk.
authors.forename: Dominic S
authors.initials: DS
authors.lastname: Wright