Metal‐Free σ‐Bond Metathesis in 1,3,2‐Diazaphospholene‐Catalyzed Hydroboration of Carbonyl Compounds

Abstract

The first metal-free catalytic hydroboration of carbonyl derivatives has been developed in which a catalytic amount of 1,3,2-diazaphospholene effectively promotes a hydroboration reaction of aliphatic and aromatic aldehydes and ketones. The reaction mechanism involves the cleavage of both the PO bond of the alkoxyphosphine intermediate and the BH bond of pinacolborane as well as the formation of PH and BO bonds. Thus, the reaction proceeds through a non-metal σ-bond metathesis. Kinetic and computational studies suggest that the σ-bond metathesis occurred in a stepwise but nearly concerted manner.

Investigation of N‐Heterocyclic Carbene‐Supported Group 12 Triflates as Pre‐catalysts for Hydrosilylation/Borylation

“…The reaction mixture was allowed to stir for 10 min at which time a0 .2 mL aliquot was taken from the reaction mixture and the volatiles were removed under vacuum. Data for (4-ClC 6 H 4 ) 2 CHOBPin [20] and MesCH 2 OBPin [38] were consistent with the literature. In as imilar manner,t he reaction was conducted with a1mol %loading of [IPr·Cd(OTf) 2 ] 2 (0.008 g, 0.005 mmol), benzophenone (0.092 g, 0.51 mmol), HBPin (73 mL, 0.51 mmol) in 2mL of THF.T he reaction was also conducted with a0 .1 mol %l oading of [IPr·Cd(OTf) 2 ] 2 (0.006 g, 0.004 mmol), benzophenone (0.681 g, 3.74 mmol), HBPin (542 mL, 3.74 mmol) and 5mLo fT HF.R elevant data are presented in Table 1.…”

“…The resulting catalytic hydroborylationr eactionw as found to be much more rapid than hydrosilylation, with the reaction going to 98 % completion after 10 min in the presenceo fa1mol %l oading of 2 (TOF = 593 h À1 ). [20] High turnover frequencies were also maintained with more sterically hindereds ubstrates. [19] and ar ecently reported diazaphospholene catalyst prepared by Kinjo and co-workers (TOF = 1.8 h À1 at 90 8C).…”

A Nucleophilicity Scale for the Reactivity of Diazaphospholenium Hydrides: Structural Insights and Synthetic Applications

“…Gudat and co-workers seminal work demonstrated that 1a is af orm of super-hydride, [3] yet with common features of organic reagents, [4] such as relatively low cost and good solubility in organic media. Consequently,an umber of N-heterocyclic phosphorus hydrides ( Figure 1) and their analogues have been developed in recent years,rendering many originally infeasible reactions to occur under metal-free conditions,s uch as reductions of polar olefins, [5] imines, [5a] ketones, [6] and azo compounds, [7] valorization of CO 2 , [8] and hydroboration of pyridines. Consequently,an umber of N-heterocyclic phosphorus hydrides ( Figure 1) and their analogues have been developed in recent years,rendering many originally infeasible reactions to occur under metal-free conditions,s uch as reductions of polar olefins, [5] imines, [5a] ketones, [6] and azo compounds, [7] valorization of CO 2 , [8] and hydroboration of pyridines.…”

P–N Cooperative Borane Activation and Catalytic Hydroboration by a Distorted Phosphorous Triamide Platform

“…The difference in substrate polarization could be expected to invert the sense of E–H addition to 1 , with hydride translocating to the phosphorus center and the attendant E + fragment migrating to ligand nitrogen. This mode of activation would result in formation of a P -hydrido-1,3,2-diazaphospholene ( C ), a class of compound that Gudat 18 has shown to exhibit significant hydridic reactivity and that Kinjo 19 and most recently Speed 20 have capitalized on in catalysis. We wished to ascertain whether interfacing these elementary reactivities with a subsequent group transfer from the pendant N -methylanilide with regeneration of 1 would permit an overall catalytic E–H transfer via a new P–N cooperative scheme.…”