Hydrogen Bonding Behavior of Amide-Functionalized α-Diimine Palladium Complexes

Abstract

A class of (N,N′-diaryl-α-diimine)Pd complexes bearing amide substituents on the N-aryl rings is described. Hydrogen bonding interactions involving the amide groups influence the structures, isomer distributions, and ligand coordination behavior of these compounds. The amidefunctionalizedwere prepared by condensation reactions of 2,3-butanedione and the appropriate anilines. The attempted preparation of (2,6-i Pr 2 -Ph)NCMeCMeN(2-C(O)NHMe-6-i Pr-Ph) (4d) yielded the corresponding 1,2dihydroquinazolinone derivative 4d′ formed by nucleophilic attack of the amide nitrogen at the proximal imine carbon. 4a and 4b react with (cod)PdMeCl to yield square planar (α-diimine)PdMeCl complexes 5a,a′ and 5b,b′, respectively, which exist as two isomers that differ in the orientation (trans/cis) of the Pd−Me ligand and the amide-substituted arylimine unit. 4c reacts with (MeCN) 2 PdCl 2 and (cod)PdMeCl to yield (4c)PdCl 2 (6c-anti,syn) and ( 4c)PdMeCl (5c-anti,syn), which exhibit anti/syn isomerism due to hindered rotation of the C aryl −N bonds. In the solid state, the amide oxygen atoms in 6c-anti and 5c-syn engage in hydrogen bonding with cocrystallized CH 2 Cl 2 solvent molecules. 4d′ reacts with (MeCN) 2 PdCl 2 via ring-opening metalation to afford the α-diimine complex (4d)PdCl 2 (6d). Transmetalation of 6d with SnMe 4 yields (4d)PdMeCl (5d,d′) as a mixture of trans and cis isomers. The reaction of 5d,d′ with AgOAc yields (4d)PdMe(OAc) (7d) as a single isomer in which the Pd−Me group is trans to the amide-functionalized arylimine unit. 5d, 6d, and 7d exhibit intramolecular N−H•••Cl and N−H•••O hydrogen bonding interactions involving the amide NH units. The reactions of 5a,a′, 5c-anti, and 5d,d′ with AgSbF 6 in the presence of pyrazole yield the corresponding (α-diimine)PdMe(pz) + SbF 6 − salts (8a,c,d; pz = pyrazole), which exhibit an intramolecular hydrogen bond between the amide oxygen and the pyrazole NH unit. 8a,c,d undergo partial dissociation of pyrazole in CD 3 CN solution to generate the corresponding CD 3 CN complexes 9a,c,d. The non-hydrogen-bonded complex {(2,6-i Pr 2 -Ph)NCMeCMeN(2,6-i Pr 2 -Ph)}PdMe(pz) + SbF 6 − (8e) and its pyrazole dissociation product {(2,6-i Pr 2 -Ph)N CMeCMeN(2,6-i Pr 2 -Ph)}PdMe(CD 3 CN) + SbF 6 − (9e) were generated in a similar fashion. The pyrazole dissociation constants, K eq = [(α-diimine)PdMe(CD 3 CN) + ] × [pz] × [(α-diimine)PdMe(pz) + ] −1 , vary in the order 8e > 8d > 8a > 8c, span more than 2 orders of magnitude, and reflect the enhancement of pyrazole binding in 8a,c,d by amide−pyrazole hydrogen bonding. The intramolecular hydrogen bonding in 8c strengthens pyrazole binding by a factor of ca. 120 (i.e., ΔΔG = 2.8(1) kcal mol −1 ) relative to the case of 8e.

Highly Robust Palladium(II) α‐Diimine Catalysts for Slow‐Chain‐Walking Polymerization of Ethylene and Copolymerization with Methyl Acrylate

“…Previously, the research groups of Jordan and Guan successfully obtained the methyl palladium(II) species by the treatment of ligands with [(MeCN) 2 PdCl 2 ], followed by methylation with SnMe 4 15a. 17 However, the reaction of ligand 2 with [(MeCN) 2 PdCl 2 ] (1 equiv) afforded multiple products in our case (see Figure S1 in the Supporting Information).…”

Critical Role of Anions in Platinum(II) Precursors upon the Structural Motifs of Six-Membered Cycloplatinated N,N′,N″-Triarylguanidines

“…The IR spectra of 1–3 revealed a pair of bands at 1622 and 1386 cm –1 ( 1 ·1/2CH 2 Cl 2 ), 1624 and 1387 cm –1 ( 2 ), and 1676 and 1393 cm –1 ( 3 ) assignable to ν a (OCO) and ν s (OCO), respectively. The Δν values of 236, 237, and 283 cm –1 indicated the presence of hydrogen-bonded monodentate OAc 55 in 1 ·1/2CH 2 Cl 2 and 2 and hydrogen-bonded monodentate TFA in 3 , respectively. The Δν values of 326, 315, 310, and 322 cm –1 for 4–7 , respectively, indicated the presence of monodentately coordinated TFA, while the Δν value of 130 cm –1 for 12 ·CH 2 Cl 2 indicated the presence of bridging bidentately coordinated TFA.…”

Copolymerization of Ethylene with Acrylate Monomers by Amide-Functionalized α-Diimine Pd Catalysts

“…The difference between ratios 1d / 1d ′ and 1e / 1e ′ corresponds to an additional stabilization in 1d by ΔΔ G = 0.9 kcal mol –1 , which is a measure of the strength of intramolecular N–H···Cl hydrogen bond in 1d . 1a is stabilized over 1b by a similar amount (ΔΔ G = 0.7 kcal mol –1 ) …”