The present paper dea
ls with the synthesis and fu
ll characterization of a series of pyridine-functiona
lized phosphine comp
le
xes of Ru(II), name
ly, RuC
l2(
Lnx)(PPh
3) (
Lnx = R
2PCH
2(C
5H
2R′R′′N)), differing in the nature of the substituents on the phosphorus (superscript
labe
l n in
Lnx defined as
n = 1 for R = Ph,
n = 2 for R = Cy) and/or on the pyridy
l group (superscript
labe
l x in
Lnx defined as
x =
a for pico
ly
l, noted pic, and
x =
b for quino
ly
l, noted quin) and disc
loses new aspects of their reactivity with respect to cata
lysis. The
ligands 2-[(dipheny
lphosphino)methy
l]-6-methy
lpyridine,
L1a, 2-[(dipheny
lphosphino)methy
l]quino
line,
L1b, 2-[(dicyc
lohexy
lphosphino)methy
l]-6-methy
lpyridine,
L2a, and 2-[(dicyc
lohexy
lphosphino)methy
l]quino
line,
L2b, were prepared and respective
ly reacted with RuC
l2(PPh
3)
3 under optimized experimenta
l conditions. In a pre
liminary test, the reaction of RuC
l2(PPh
3)
3 with
L1a using a stoichiometric 1/1 meta
l/
ligand ratio gave three comp
le
xes, name
ly, [RuC
l2(PPh
3)
2]
2 (
1), [(PPh
3)
2C
lRu(μ-C
l)
3Ru(
L1a)(PPh
3)] (
21a), and RuC
l2(
L1a)
2 (
31a). These were iso
lated by fractiona
l crysta
llization and, at that stage, identified on
ly by sing
le-crysta
l X-ray diffraction. The formation of
1 and
21a ref
lects the existence of the e
lusive 14 e
− fragment “RuC
l2(PPh
3)
2”, which tends to re
lieve its unsaturation by intermo
lecu
lar association. By contrast, contro
lled addition of 2-(phosphinomethy
l)pyridine type
ligands
Lnx to RuC
l2(PPh
3)
2 leads se
lective
ly to the desired 16 e
− species RuC
l2(
Lnx)(PPh
3) (
4nx). For examp
le, with
L1b, the green comp
lex RuC
l2(
L1b)(PPh
3) (
41b-trans-Cl) was identified as the kinetic product of
ligand addition. It s
low
ly and irreversib
ly converts into the more stab
le isomer RuC
l2(
L1b)(PPh
3) (
41b-cis-Cl), representing the thermodynamic product. Both isomers were fu
lly characterized by NMR spectroscopy and X-ray diffraction. Simi
lar transformations, taking p
lace at different rates, were observed within the
ligand series examined here. A
ll isomeric forms of type
4na comp
le
xes react c
lean
ly with a termina
l a
lkyne-
like pheny
lacety
lene to give a new comp
lex identified by NMR spectroscopy as the viny
lidene species RuC
l2(
L)(CCHPh)(PPh
3) (
5na). The reaction of
4nb-cis-Cl with an excess of ethy
l diazoacetate at –60 °C gives the nove
l comp
lex RuC
l2(
Lna){
cis-EtO(O)C(H)C
C(H)C(O)OEt} (
6na) with concomitant e
limination of the phosphonium y
lide, Ph
3P
C(H)C(O)OEt. Whereas 1 equiv of diazoa
lkane thus serves as phosphine scavenger, the uptake of two more carbene units by the remaining 14 e
− fragment “RuC
l2(
L1a)” resu
lts in their coup
ling, providing diethy
l ma
leate, intercepted in
6na as a coordinated
ligand. Pre
liminary cata
lytic tests indicate that the comp
le
xes
4nx act as cata
lyst precursors for the ROMP of norbornene in the presence of trimethy
lsi
ly
ldiazomethane as the carbene source. The same compounds
4nx are a
lso used as cata
lyst precursors in the transfer hydrogenation of a series of ketone substrates using a
lcoho
l as the hydrogen source. For examp
le, the hydrogenation of cyc
lohexanone is achieved in 99% yie
ld within 45 s with on
ly 0.01 mo
l (0.1 mo
l %) of the precata
lyst RuC
l2(Ph
2PCH
2pic)(PPh
3)
-trans-Cl (
41a), representing a turnover frequency of 272 571 h
−1. The X-ray structure ana
lyses of
1,
21a,
31a,
41b (both
trans-C
l and
cis-C
l isomers), and
61a are reported.