Synthesis of Functionalized Hydrazines: Facile Homogeneous (N‐Heterocyclic Carbene)‐Palladium(0)‐Catalyzed Diboration and Silaboration of Azobenzenes

Abstract

The bis(N‐heterocyclic carbene)(diphenylacetylene)palladium complex [Pd(ITMe)2(PhC≡CPh)] (ITMe=1,3,4,5‐tetramethylimidazol‐2‐ylidene) acts as a highly active pre‐catalyst in the diboration and silaboration of azobenzenes to synthesize a series of novel functionalized hydrazines. The reactions proceed using commercially available diboranes and silaboranes under mild reaction conditions.

Direct Synthesis of Indoles from Azoarenes and Ketones with Bis(neopentylglycolato)diboron Using 4,4′-Bipyridyl as an Organocatalyst

“…13 C­{ 1 H} NMR (100 MHz, C 6 D 6 ): δ 147.6, 128.9, 121.2, 118.4, 72.6, 31.8, 21.5. The NMR data were consistent with the reported data …”

“…13 C­{ 1 H} NMR (100 MHz, CDCl 3 ): δ 134.6, 132.0, 128.7, 126.5, 122.8, 117.5, 110.4, 108.5, 52.6, 51.9, 45.9, 24.0, 21.6. The NMR data were consistent with the reported data . Preparation of 3cv in gram-scale reaction: (step 1) in an oven-dried J-young Schlenk (100 mL) containing a magnetic stirring bar, 1,2-bis­( p -tolyl)­diazene ( 1c , 10.0 mmol, 2.1 g), B 2 nep 2 (22 mmol, 4.9 g), 4,4′-bipyridyl (0.40 mmol, 62.5 mg), and toluene (10 mL) were added.…”

Activation of the Si–B interelement bond related to catalysis

“…A palladium-catalysed silaboration of azobenzenes was described by Spencer and co-workers in 2016 (202a-d -203a-d, Scheme 65). 87 The resulting functionalised hydrazines are stable towards air and moisture and are easily purified by filtration after precipitation from water. Unsymmetric azobenzenes were compatible in this transformation but led to mixtures of regioisomers (not shown).…”

Synthesis of trans-Mono(silyl)palladium(II) Bromide Complexes

“…A possible mechanism for the formation of 2 includes either a σ-bond metathesis between a Pd-Si, in cis -[Pd(ITMe) 2 (SiR 3 ) 2 ], and Br-C bond, in allylbromide, or an S N 2/S N 2′ by the nucleophilic Pd-Si bond at the electrophilic sites in the allyl halide, leading to a trans complex. As we have previously suggested using computational studies on related bis-ITMe complexes, an NHC would then dissociate from the palladium center followed by a cis to trans isomerization of the Br and Si moieties ( Scheme 2 ) [ 11 ]. Finally, the dissociated NHC would re-coordinate, constrained by the bulk of the other ligands, in a cis -configuration [ 16 , 17 ].…”

“…Analogues have been used in silyl-Negishi couplings [ 8 ]. We wish to report here our preliminary findings on the reaction of (ITMe) 2 Pd(silyl) 2 complexes with allyl bromide (ITMe = 1,3,4,5-tetramethylimidazol-2-ylidene) [ 9 , 10 , 11 , 12 ].…”