[6,5] CNN Palladium(II) Pincer Complexes Containing N-Substituted Monoanionic and Dianionic Guanidinate Ligands: Syntheses, Structural Aspects, and Their Utility in Suzuki–Miyaura Coupling Reactions

Abstract

The reactions of guanidines [(ArNH)(ArN)CN-(H)(C(O)Py-2)] (Ar = 2-RC 6 H 4 ; R = Me (1) and CF 3 (2)) with Pd(OC(O)R′) 2 (R′ = Me, t Bu and CF 3 ) were studied with a view aimed at understanding the influence of substituent effects upon the nature of the resulting products. The reactions of 1 with Pd(OC(O)R′) 2 (R′ = Me and CF 3 ) in toluene at 65 °C afforded [Pd{κ 3 (C,N,N)}(OC(O)R′)] (R′ = Me (3) and CF 3 (4)), while the analogous reaction involving 1 and Pd(OC(O) t Bu) 2 afforded [Pd{κ 3 (C,N,N)}(μ-OC(O) t Bu)Pd{κ 3 (C,N,N)}] (5). The analogous reactions of 2 with Pd(OC(O)R′) 2 (R′ = Me, t Bu and CF 3 ) afforded [Pd{κ 3 (C,N,N)}(μ-OC(O)R′)Pd{κ 3 (C,N,N)}] (R′ = Me (6) and t Bu (7)) and [Pd{κ 3 (C,N,N)}(OC(O)CF 3 )] (8), respectively. Complexes 5−7 were treated with 2 equiv of Lewis bases, L at RT to afford [Pd{κ 3 (C,N,N)}(L)] [L = PPh 3 (9), 4-aminopyridine (10 and 11), and MeCN (12)]. The mechanisms of formation of new complexes were proposed. Complex 3 was treated with 12 in the presence of excess of NaOC(O) t Bu in CHCl 3 under reflux condition to afford a mixed Pd(II) pincer, [Pd{κ 3 (C,N,N)}(μ-OC(O) t Bu)Pd{κ 3 (C,N,N)}] (15), and this observation indirectly supports the mechanism proposed for the formation of 5−7. The mechanisms of formation of 9−12 were verified by in situ reaction involving 7 and PPh 3 (1 and 2 equiv) through 19 F NMR spectroscopy. The new compounds were fully characterized, and molecular structures of 1, 3•C 7 H 8 , 4−6, 8•C 7 H 8 , 9, and 10•H 2 O were determined by SCXRD. The CNN tridentate guanidinate ligands were present in monoanionic (3•C 7 H 8 , 4 and 8•C 7 H 8 ), mono-and dianionic (5 and 6), and dianionic (9 and 10•H 2 O) forms, and hence the structures of 5 and 6 are unprecedented. Complex 3•C 7 H 8 was used as an efficient catalyst in Suzuki−Miyaura reactions involving sterically hindered aryl bromides and aryl boronic acids.

Palladium(II) Pincer Complexes Derived From N,N’,N’’‐Tris(2‐thioanisyl)guanidine. Syntheses, Structural Aspects, Solution Behaviour and Suzuki‐Miyaura Coupling Reactions

“…4‐Bromoanisole and phenylboronic acid were coupled in the presence of 0.1 mol% of 2 , 3 and 4 by following the optimized condition previously reported for V [23] (See Figure 6, Table 3, entries 1–3). It was found that 2 was the most active catalyst among 2 – 4 .…”

“…General Procedure for Optimization of Catalysts and Base in Suzuki‐Miyaura Coupling Reactions The procedure adopted for optimization of catalysts and base is same as that we reported previously for Suzuki‐Miyaura coupling reactions involving 4‐bromoanisole and PhB(OH) 2 [23] except that the catalyst quantity used in the present study is 0.1 mol%.…”

“…General Procedure for Suzuki‐Miyaura Coupling Reactions The procedure adopted for Suzuki‐Miyaura coupling reactions involving various aryl bromides and arylboronic acid is same as that reported previously for Suzuki‐Miyaura coupling reactions involving aryl bromides and arylboronic acids [23] …”

“…For sometimes, we have been interested in designing a robust Pd(II) guanidine adducts and cyclopalladated guanidinate(1-) complexes for CÀ C bond forming reactions such as Suzuki-Miyaura and Heck-Mizoroki coupling reactions. [23,[32][33][34] The results obtained from our laboratories encouraged us to explore the utility of 2-4 as catalysts in Suzuki-Miyaura coupling reactions.…”

Cobalt(II)-Catalyzed Directed C–H Functionalization/[3+2] Annulation of N-Arylguanidines with Alkynes

“…Guanidine 3 has been chosen as one of the substrates for C− H functionalization/annulation (Figure 1c). 15 The reactions of 2-picolylamine with N,N′-di(2-tolyl)-and N,N′-bis(2-trifluoromethylphenyl)-carbodiimides carried out separately in Et 2 O at rt afforded 4 and 5 in good yields (See Scheme 1). 8-Aminoquinoline (AQ) is one of the powerful DGs in metalcatalyzed C−H functionalization.…”