Platinum boryl complex

In relation to the mechanistic proposal, an interesting reactivity of (boryl)(silyl)platinum(n) complex has been reported.223 The complex is prepared by the reaction of silylborane with Pt(cod)2 complex via oxidative addition (Scheme 46). The (boryl)(silyl)platinum complex undergoes insertion of alkynes at the B-Pt bond to give (/3-borylalkenyl)(silyl)platinum(n) complex in high yield. Importantly, the insertion takes place regioselectively, with Pt-G bond formation at the internal. -carbon atom. This result may indicate that the boron-transition metal bond is more prone to undergo insertion of unsaturated molecules. 

The reaction of the T-shaped three coordinate platinum boryl complex trans-[ Cy3P)2Pt B(Br)Fc ] [BAr 4] (21) (Fc = ferrocenyl) with 4-methylpyri-dine leads to the formation of trans-[(Cy3P)2Pt(Br) B(Fc)(NC5H4Me-4) ]... 

Table 12 Selected data for structurally characterized platinum boryl complexes...

Fig. 36 Crystallographically characterized square planar platinum(II) bis(boryl) complexes 10.16-10.30...

Insertion into metal boryl bonds is represented by two examples described for a late and an early transition metal complexes. Platinum diboryl complexes react with alkynes to give the diborylated alkene (Scheme 6.61, a) [191]. A titanium(II) metallocene with a coordinated ethylene reacts with borane to give, via insertion of the alkene into a M-B bond and subsequent j6-H ehmination, a complex with a coordinated vinylborane (Scheme 6.61, b) [192]. Both processes can be made catalytic. 

Let us take acrolein as an example to illustrate the findings from the DFT calculations. For a platinum boryl complex (37), the boryl ligand can act as a nucleophile if the Pt-boryl o-bonding electron pair plays the role to initiate the reaction and as an electrophile if the empty p orbital to initiate the reaction. Scheme 9 shows three possible insertion pathways for the reaction of the bis-boryl diimine platinum(II) complex with acrolein whose a -electron density distribution is also illustrated in 37. The free energy barriers for the pathways of the boryl attacks at C4 and C2 were calculated to be 35.7 and 53.3 kcal/mol, respectively [106]. Interestingly, the free energy barrier for the pathway of the boryl attack at O was calculated to be only 18.6 kcal/mol [106]. These results indicate that the boryl ligand, in this case, behaves as an electrophile. 

Diboration of a,/ -unsaturated ketones is promoted by platinum(O) complexes. Reaction of 4-phenyl-3-buten-2-one with bis(pinacolato)diboron in the presence of a platinum catalyst affords a boryl-substituted (Z)-boron enolate, that is, a 1,4-diboration product, in high yield with high stereoselectivity (Scheme 8). The isolated boron enolate is easily hydrolyzed by exposure to water, giving / -boryl ketones in high yields.66 Similar diboration of a,/ -unsaturated ketones has also been achieved with Pt(bian)(dmfu) (bian = bis(phenylimino)acenaphthene, dmfu = dimethyl fumarate).67 Although the... 

For each case we will also present catalytic analogues, namely (1) the activation of methane to form methanol with platinum, the reaction of certain aromatics with palladium to give alkene-substituted aromatics, and (2) the alkylation of aromatics with ruthenium catalysts, and the borylation of alkanes and arenes with a variety of metal complexes. 

Heteroalkenes, with iron, 6, 132 Heteroannulation, allylic benzylamines, 10, 156 Heteroarene chromium carbonyls, preparation and characteristics, 5, 260 Heteroarenes borylation, 10, 242 C—H functionalizations, 10, 127 as metal vapor synthesis milestone, 1, 237 with titanium, 4, 246 vanadium complexes, 5, 48 7]6-Heteroarenes, with platinum, 8, 664 Heteroaromatic compounds... 

In 1993, Ishiyama et al.60 reported the synthesis of isomerically pure cis-1,2-bis(boryl)alkenes 53a-57a from their corresponding alkynes 53-57 (Scheme 12)60,61 via platinum complexes. The solvents did not play an important role in the reaction, but a comparison of the reaction rates at 50 °C revealed that the addition was apparently accelerated in polar... 

Borylation of 1-alkenyl iodides and triflates with HBpin was catalyzed by palladium catalyst in the presence of Et3N (Equation (61)).330 Platinum(0)-AsPPh3 complexes catalyzed the borylation of allyl chlorides (Equation (62)).331,332... 

C—H borylation of indoles has been reported by a number of groups. Chirik and coworkers utilized pincer-ligated cobalt complexes with N-methyhndole and recorded the C-2 borylated indole (133) as the major product (2014JAC4133). The catalysts employed demonstrated high catalysis turnover and low catalytic loading and also demonstrated efficacy with other electron-rich heteroarenes (furan, thiophene, benzofuran) as well as electron-deficient pyridines. More recendy, platinum-NHC complexes have been used in the selective C—H borylation of indoles (2015JAC12211). The authors reported higher isolated yields with this... 

---