A Facile Route to Aryl Boronates: Room-Temperature, Copper-Catalyzed Borylation of Aryl Halides with Alkoxy Diboron Reagents

π-Face donation from the aromatic N-substituent of N-heterocyclic carbene ligands to metal and its role in catalysis

In this work, we calculate the redox potential in a series of Ir and Ru complexes bearing a N-heterocyclic carbene (NHC) ligand presenting different Y groups in the para position of the aromatic N-substituent. The calculated redox potentials excellently correlate with the experimental ΔE(1/2) potentials, offering a handle to rationalize the experimental findings. Analysis of the HOMO of the complexes before oxidation suggests that electron-donating Y groups destabilize the metal centered HOMO. Energy decomposition of the metal-NHC interaction indicates that electron-donating Y groups reinforce this interaction in the oxidized complexes. Analysis of the electron density in the reduced and oxidized states of representative complexes indicates a clear donation from the C(ipso) of the N-substituents to an empty d orbital on the metal. In case of the Ru complexes, this mechanism involves the Ru-alkylidene moiety. All of these results suggest that electron-donating Y groups render the aromatic N-substituent able to donate more density to electron-deficient metals through the C(ipso) atom. This conclusion suggests that electron-donating Y groups could stabilize higher oxidation states during catalysis. To test this hypothesis, we investigated the effect of differently donating Y groups in model reactions of Ru-catalyzed olefin metathesis and Pd-catalyzed C-C cross-coupling. Consistent with the experimental results, calculations indicate an easier reaction pathway if the N-substituent of the NHC ligand presents an electron-donating Y group.

Carbon-boron bond cross-coupling reaction catalyzed by -PPh(2) containing palladium-indolylphosphine complexes

This study describes the application of indolylphosphine ligands with a diphenylphosphino moiety to the palladium-catalyzed borylation of aryl chlorides. The combination of palladium metal precursor with PPh(2)-Andole-phos, which comprises an inexpensive -PPh(2) group, provides highly effective catalysts for the borylation of aryl chlorides. A range of functional groups such as -CN, -NO(2), -CHO, -COMe, -COOMe, and -CF(3) was compatible, and the catalyst loading down to 0.025 mol % of Pd can be achieved. The Pd/PPh(2)-Andole-phos system is able to catalyze both borylation reaction and Suzuki-Miyaura coupling reaction in a one-pot sequential manner for the direct synthesis of biaryl compounds in excellent yields.

Cu(I)-catalyzed (11)C carboxylation of boronic acid esters: a rapid and convenient entry to (11)C-labeled carboxylic acids, esters, and amides

Rapid and direct: the carboxylation of boronic acid esters with (11)CO(2) provides [(11)C]carboxylic acids as a convenient entry into [(11)C]esters and [(11)C]amides. This conversion of boronates is tolerant to diverse functional groups (e.g., halo, nitro, or carbonyl).

2,2'-(3,3'-Dihexyl-2,2'-bithio-phene-5,5'-di-yl)bis-(4,4,5,5-tetra-methyl-1,3,2-dioxaborolane)

In the title mol-ecule, C(32)H(52)B(2)O(4)S(2), the two thio-phene rings are twisted by 67.34 (2)°. In the crystal, weak C-H⋯O hydrogen bonds link mol-ecules related by translation along the a axis into chains.

Copper-catalyzed trifluoromethylation of aryl boronic acids using a CF3+ reagent

A copper-catalyzed process for trifluoromethylation of aryl, heteroaryl, and vinyl boronic acids has been developed. The reaction is conducted under mild conditions and shows tolerance to moisture and a variety of functional groups.

Miyaura Borylations of Aryl Bromides in Water at Room Temperature

New technology for palladium-catalyzed cross-couplings between B2pin2 and aryl bromides leading to arylboronates is described. Micellar catalysis serves to enable borylations to take place in water as the only medium at ambient temperatures.

Neopentylglycolborylation of ortho-substituted aryl halides catalyzed by NiCl(2)-based mixed-ligand systems

NiCl(2)-based mixed-ligand systems were shown to be very effective catalysts for the neopentylglycolborylation of aryl iodides, bromides, and chlorides bearing electron-rich and electron-deficient ortho-substituents. Although NiCl(2)-based single-ligand catalytic systems were able to mediate neopentylglycolborylation of selected substrates, they were not as effective for all substrates, highlighting the value of the mixed-ligand concept. Optimization of the Ni(II)-catalyzed neopentylglycolborylation of 2-iodoanisole and methyl 2-iodobenzoate demonstrated that, while the role of ligand and coligand in the conversion of Ni(II) precatalyst to Ni(0) active catalyst cannot be ignored, a mixed-ligand complex is likely present throughout the catalytic cycle. In addition, protodeborylation and hydrodehalogenation were demonstrated to be the predominant side reactions of Ni(II)-catalyzed borylation of ortho-substituted aryl halides containing the electron-deficient carboxylate substituents. Ni(II) complexes in the presence of H(2)O and Ni(0) are responsible for the catalysis of these side reactions.

Flexibility of N-heterocyclic carbene ligands in ruthenium complexes relevant to olefin metathesis and their impact in the first coordination sphere of the metal

We present a detailed static and dynamics characterization of 11 N-heterocyclic carbene (NHC) ligands in Ru complexes of the general formula (NHC)Cl(2)Ru horizontal lineCH(2). Analysis of the dynamic trajectories indicates that the nature of the N substituent can result in extremely different flexibilities of the Ru complexes. In almost all the cases the N substituent trans to the Ru-ylidene bond is severely folded so that it protects the vacant coordination position at the Ru center. Limited flexibility is instead associated with the N substituent on the side of the Ru-ylidene bond. NHCs with a single ortho substituent, either a simple Me or a bulkier i-Pr group, have a preferential folding that bends the unsubstituted side of the ring toward the halide-Ru-halide plane. Analysis of the dynamics trajectories in terms of buried volume indicates that the real bulkiness of these systems can be somewhat modulated, and this flexibility is a key feature that allows NHCs to modulate their encumbrance around the metal in order to make room for bulky substrates. Analysis of the buried volume in terms of steric maps showed that NHCs with mesityl or 2,6-diisopropylphenyl N substituents have quite different reactive pockets: rather flat with constant pressure on the halide-Ru-halide plane in the former and vault-shaped with higher pressure on the sides in the latter. Regarding the NHCs with an ortho tolyl or i-Pr group on the N substituent, the steric maps quantify the higher impact of the unsubstituted side of the ligand in the first coordination sphere of the metal and evidence the overall C(s)- and C(2)-symmetric reactive pockets of the corresponding complexes. We believe that a detailed characterization of the differently shaped reactive pockets is a further conceptual tool that can be used to rationalize the experimentally different performances of catalysts bearing these ligands or to devise new applications.