Bidentate ligands of the type Mes*PC(R)Py
((E)-
2, R = H; (Z)-
9, R
= SiMe3; Mes* =
supermesityl = 2,4,6-tri-tert-butylphenyl; Py =
2-pyridyl) were synthesized. Ligand
(E)-
2
was synthesized by reacting
Mes*P(Li)SiMe2(t-Bu)
(4) with 2-pyridinecarboxaldehyde.
Ligand (Z)-
9 was synthesized via a
PdCl2(dppb)-catalyzed coupling reaction
between
2-bromopyridine and Mes*PC(SiMe3)M
((E)-
7, M = ZnCl; (Z)-
8,
M = MgBr). Compound
(E)-
2 was also characterized by an X-ray crystal
structure determination; it has a planar
structure with the (E)-configuration. The complexes
η1,η1-[Mes*PC(R)Py]PdCl2
(11, R =
H; 12, R = SiMe3) were prepared by the
reaction of bis(benzonitrile)palladium
dichloride
with (E)-
2 and (Z)-
9,
respectively. The complexes
η1,η1-[Mes*PC(R)Py]MePdCl
(13, R =
H; 14, R = SiMe3) were obtained by a ligand
exchange reaction of MePdCl(COD) with
(E)-
2
and (Z)-
9, respectively. Complex
13 was alternatively prepared by reaction of 11
with
methylmagnesium chloride. Complex 14 was unambiguously
identified by an X-ray crystal
structure determination. Both 13 and 14
reacted with CO, resulting in the acetyl complexes
η1,η1-[Mes*PC(R)Py]AcPdCl (16, R =
H; 17, R = SiMe3).
Novel functionalized phosphaalkene-based bidentate ligands of the type 1-[(E)-Mes*PC(H)]-3-R-benzene (8, R = N-phenylcarbaldimino; 2, R = 2-pyridyl; Mes* = 2,4,6-tri-tert-butylphenyl) were prepared via a Pd(0)-catalyzed cross-coupling reaction of (Z)-bromophosphaalkene (Z)-
1 with Grignard reagents. The reaction of 8 and 2 with MePdCl(COD)
furnished three-membered phosphapalladacycles of the type
(9, R = N-phenylcarbaldimino; 10, R = 2-pyridyl), displaying intramolecular coordination
between the phosphine ligand and palladium(II). The structure of 10 was established by an
X-ray structure determination, showing a dimeric structure. The addition of triphenylphosphine to 9 and 10 causes rupture of the interconnecting Pd−N bonds, furnishing 11 and 12,
respectively.
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