Bonding in square-planar MCl(CX)[P(i-Pr)3]2 complexes of rhodium and iridium (X = O and CH2) studied by UV photoelectron spectroscopy and DV-Xα calculations

A series of new fluororhodium(I) complexes †

“…Since it has been observed both by van Gaal and McFarlane and coworkers 18 that in square-planar rhodium() compounds having two tertiary phosphines in trans disposition the increase in the effective electronegativity at the metal leads to an increase in the size of J(RhP), the decrease of the 103 Rh-31 P coupling constants in the spectra of 3a,3b and 6-9 may be due to a decrease of the π-acceptor ability of the ligands LЈ by going from the left to the right in the above-mentioned series. Recent electrochemical measurements suggest that in complexes of the type trans-[RhCl(LЈ)(PPr i 3 ) 2 ] the π-acceptor ability decreases in the order CO > C᎐ ᎐ CPh 2 > C 2 H 4 , 19 whereas with respect to carbon monoxide and vinylidene both UV photoelectron spectra and DV-Xα calculations point to a higher π-acceptor ability for C᎐ ᎐ CH 2 than for CO. 20 The IR spectra of complexes 3a,3b and 6-9 exhibit one band between 425 and 470 cm Ϫ1 with medium intensity which is assigned to the Rh-F stretching frequency. The band lies in the same region as that of other fluororhodium complexes such as trans-[RhF(CO)(PCy…”