Pt-NHC complex

Scheme 5.22 Reductive cychsation of diynes or enynes catalysed by NHC-Pt complex...

While the NHC-Ni-mediated catalysis has attracted a considerable interest in organic chemistry for several decades, the development of complexes NHC Pt is much more recent. Several examples of NHC-Pt complexes are shown in Figure 10.3. 

V,5 -NHC ligands. Additionally, Hahn and co-workers disclosed the preparation of Pt complexes bearing phosphine/benzimidazol-2-ylidene as ligands. Certainly, the most popular application of [(NHC)Pt] complexes to date is the hydrosilylation reactions. However, these are covered in Chapter 13... 

Reductive cyclization of diynes or enynes was catalyzed by NHC-Pt complexes in the presence of H2 and SnCl2 as activator (Equation (10.33)) to afford an interesting pathway to 2,5-dihydrofurans, pyrroles or cyclopentenes in moderate to good yields (50-88%). ° ... 

In 2009, Marinetti and co-workers reported the preparation and structural data of NHC-Pt complexes and their catalytic activity in model 1,6-enyne cycloisomerization reactions. The elaboration of square-planar Pt complexes... 

On the other hand, regioselective H-B addition reaction to vinylarenes and alkynes mediated by this NHC-Pt complex was also reported (Equation... 

The in situ generated 81 was the most efficient NHC-Pt complex for the hydrosilylation of styrene with triethylsilane (Figure 13.12). A high yield (99%) and selectivity (82.5 17.2 0.3, p/a/dehydrogenative respectively) towards the desired product were the most attractive aspects of the catalyst. 

A variety of NHC Pt complexes 82 were studied by Hor and co-workers, although, the activity and selectivities were considerably lower than for NHC-Pt eomplexes (Figure 13.13). " Complex 82 was highly selective for the formation of the a-isomer in the hydrosilylation of phenylacetylene with bis (trimethylsilyloxy)methylsilane. Bis-carbene derivative 83 selectively afforded the p-(. -isomer (25 41 15 19, p-( )/p-(Z)/a/dehydrogenative), whereas 84 behaved similarly to 82 but less efficiently. 

On the other hand, the study of a heteroaryl-NHC-p-diketone combination in a cyclometallated NHC-Pt complex " (Figure 10.11) showed that the observed emission was mainly based on the NHC ligand, with a significant metal eontribution. Then, the tuning of photophysical properties can be obtained by a simple ehange in the nature and size of substituent groups as well as the size of the n-system. 

Over time, NHC-Pt eomplexes with inereasingly sophistieated molecular scaffolds have been reported, such as poly-NHC-Pt complexes, mixed imi-noboryl-NHC-Pt complex, NHC-Pt moleeular square, bis(NHC)cyclo-phane-Pt complex, polynuelear complexes, as well as NHC-mixed metal complexes containing PtM2-metallocyclopropane units or original dou-ble-NHC-Pt complex salt (Figure 10.12). 

On the other hand, Thomas highlighted a C-H activation mechanism (experimental, spectroscopic and computational studies) leading to active NHC-Pt hydride complexes. Conejero and co-workers studied the reactivity of cationic bis(NHC)-Pt complexes, bearing a cyclometallated NHC ligand, while De Jesus and co-workers described water-soluble [(NHC)Pt] complexes substituted with sulfonatoalkyl moities. ... 

In 2009, Marinetti and co-workers reported the preparation and structural data of NHC-Pt" complexes and their catalytic activity in model 1,6-enyne cycloisomerization reactions. The elaboration of square planar Pt" complexes bearing symmetric or unsymmetric chiral diphosphines was described in a sequence involving an iodine oxidative addition to a NHC-Pt complex and subsequent complexation of a chiral chelating diphosphine. In this context, the synthesis of a new family of Pt" six-membered metallacyclic NHC complexes was reported. This new platinacyclic complex was then used in an enantioselective 1,6-enyne cycloisomerization to afford, under mild conditions, the expected fused azabicycles in very high enantiomeric excesses and good to excellent yields [eqn (10.45)]. 

Marko and co-workers reported the activity of monomeric, moisture and air-stable NHC-Pt such as 133 (Figure 13.15). When complex 133 was applied to the hydrosilylation of a variety of terminal alkenes, only the anti-Markovnikov adducts were obtained, with isomerization by-products representing less than 2% of the reaction products. This catalyst tolerated functional groups such as ethers, carbonyls and esters, but internal alkenes were inert under similar conditions. A related series of six- and seven-mem-bered ring-expanded NHC-Pt complexes 134 was tested in the hydrosilylation of 1-octene with bis(trimethylsiloxy)methylsilane excellent activity and regioselectivity were observed. ... 

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