- Remarkable catalytic property of nanoporous gold on activation of diborons for direct diboration of alkynes
-
A novel catalytic property of nanoporous gold for activation of bis(pinacolato)diboron has been reported that allows the direct diboration of alkynes to proceed sufficiently in a heterogeneous process. The experimental results revealed that the nanoporous gold catalyst is able to cleave the B-B bond of bis(pinacolato)diboron without using any additives.
- Chen, Qiang,Zhao, Jian,Ishikawa, Yoshifumi,Asao, Naoki,Yamamoto, Yoshinori,Jin, Tienan
-
-
Read Online
- Platinum(0)-catalyzed diboration of alkynes with tetrakis(alkoxo)diborons: An efficient and convenient approach to cis-bis(boryl)alkenes
-
Tetrakis(methoxo)- or bis(pinacolato)diboron [(RO)2BB(OR)2; (RO)2 = (MeO)2 (4a) and Me4C2O2 (1)] added to both terminal and internal alkynes in the presence of a catalytic amount of Pt(PPh3)4 to provide stereodefined cis-bis(boryl)alkenes (3) in excellent yields. Because reagents and reaction conditions were sufficiently mild, the procedure was readily extended to various functionalized alkynes. Mechanistic study revealed that the oxidative addition of bis(pinacolato)diboron (1) to Pt(PPh3)4 generates cis-Pt(BO2C2Me4)2(PPh 3)2 (5), whose structure was fully characterized by multinuclear NMR spectroscopies as well as single-crystal X-ray diffraction analysis. Complex 5 exhibited high reactivity for insertion to the alkyne giving 3 in high yields, thus implying that the oxidative addition of the B-B bond to a Pt(0) complex is an initial step in the platinum(0)-catalyzed diboration of alkynes.
- Ishiyama, Tatsuo,Matsuda, Nobuo,Murata, Miki,Ozawa, Fumiyuki,Suzuki, Akira,Miyaura, Norio
-
-
Read Online
- Ladder-type conjugated oligomers prepared by the Scholl oxidative cyclodehydrogenation reaction: Synthesis, characterization and application in field effect transistors
-
Two novel well defined ladder-type conjugated oligomers have been successfully designed and synthesized through a solution processing method in an excellent yield. The field effect transistors (FETs) fabricated by these ladder-type oligomers with a nice planar structure exhibit excellent charge carrier mobilities, up to 0.10 cm2 V-1 s-1 and 0.33 cm2 V-1 s-1; furthermore, the devices can work well with a low gate voltage. The ladder-type oligomers are both converted from two precursor co-oligomers, poly(2,7-(1,2,-diphenylethene)-9,9-dioctylfluorene) (PDPF), via an anhydrous FeCl3 oxidative cyclodehydrogenation. The pronounced red shift shown in the preliminary photoluminescence spectra and the changes of band gaps measured by electrochemical analysis both testify that the better electronic transmission capacity in the FET performance is due to the expanded molecular chain planarization after the chemical cyclodehydrogenation. Interestingly, the precursor oligomers having a linear-type chain and a zigzag-type chain (L-PDPF and Z-PDPF, respectively) show many characteristic differences in their thermal, optical and electrochemical properties. The differences caused by the different types of main chains demonstrate that the macromolecular configurations have a tremendous impact on the functioning of the oligomers.
- Huang, Wei,Zhang, Hejian,Ma, Ji,Chen, Moyun,Zhu, Haoyun,Wang, Weizhi
-
-
Read Online
- One-pot synthesis of α,α-difluoroimines from alkynes through tandem catalytic diboration/fluorination/imination reaction
-
Tandem catalytic diboration/fluorination/imination of arylacetylenes leads to the formation of α,α-difluoroimines, where the adjacent C{double bond, long}N and C-F2 bonds are formed simultaneously. The convenient one-pot protocol involves a Pt(0)-catalyzed diboration of terminal or internal arylalkynes followed by electrophilic fluorination with Selectfluor in the presence of primary amines and a dehydrating agent. A plausible mechanism for the three consecutive steps (diboration/fluorination/imination) is suggested in accordance with the electronic properties of the substrates. Alkynes/catalytic diboration/alkenyl diboronate esters/Selectfluor/electrophilic fluorination/α,α-difluoroimines.
- Ramírez, Jesús,Fernández, Elena
-
-
Read Online
- Synthesis of bis-BN-Naphthalene-Fused Oxepins and Their Photoluminescence including White-Light Emission
-
A series of novel bis-BN-naphthalene-fused oxepin derivatives were synthesized via a Pd-catalyzed tandem reaction from brominated 2,1-borazaronaphthalenes and cis-bis(boryl)alkenes. X-ray crystallographic analysis revealed that bis-BN-naphthalene-fused oxepins feature a planar framework. The electronic and photophysical properties of the novel BN-naphthalene-fused oxepins were investigated by UV-vis and fluorescence spectroscopies and density functional theory (DFT) calculations, which disclosed the distinct electronic and photophysical properties of the analogous hydrocarbon system. Interestingly, dual-fluorescent emissions were observed upon dissolving N-substituted derivatives 10-14 in dimethyl sulfoxide. Tunable emission colors especially for white-light emissions can be achieved by controlling the ratio of solvents, concentration, or temperature using only a single-molecule compound.
- Tian, Dawei,Li, Qian,Zhao, Yifan,Wang, Zijia,Li, Wenbin,Xia, Shuling,Xing, Siyang,Zhu, Bolin,Zhang, Jianying,Cui, Chunming
-
-
Read Online
- Mixed Diboration of Alkynes Catalyzed by LiOH: Regio- and Stereoselective Synthesis of cis-1,2-Diborylalkenes
-
A diboration of terminal alkynes with an unsymmetrical diboron reagent pinBBdan has been achieved using LiOH as the catalyst in the presence of stoichiometric amounts of MeOH, affording 1,2-diborylalkenes with different boryl groups. The reaction proceeds in a highly regio- and stereoselective manner through cis-addition of pinBBdan to the C-C triple bond, with the Bdan moiety being incorporated at the internal position. By taking advantage of the different reactivities of the two boryl groups, the mixed diboration product can undergo the sequential, chemoselective cross-couplings with aryl bromides to form trisubstituted alkenes.
- Peng, Sihan,Liu, Guixia,Huang, Zheng
-
-
Read Online
- An experimental and theoretical study into the facile, homogenous (N-heterocyclic carbene)2-Pd(0) catalyzed diboration of internal and terminal alkynes
-
Pd(ITMe)2(PhCCPh) acts as a highly reactive pre-catalyst in the unprecedented homogenous catalyzed diboration of terminal and internal alkynes, yielding a number of novel and known syn-1,2-diborylalkenes in a 100% stereoselective manner. DFT calculations suggest that a similar reaction pathway to that proposed for platinum phosphine analogues is followed, and that destabilization of key intermediates by the NHCs is vital to the overall success for the palladium-catalyzed B-B addition to alkynes.
- Ansell, Melvyn B.,Menezes Da Silva, Vitor H.,Heerdt, Gabriel,Braga, Ataualpa A. C.,Spencer, John,Navarro, Oscar
-
-
Read Online
- Dehydrogenative Diboration of Alkynes Catalyzed by Ir/CO/tBuNC System
-
Catalytic dehydrogenative diboration (DHDB) of alkyne with HBpin was achieved using [Ir(COD)Cl]2 and other related Ir precursors under CO atmosphere. The selectivity for DHDB over hydroboration was higher in less polar solvents and under higher
- Lai, Qingheng,Ozerov, Oleg V.
-
-
- Configuration-controllable synthesis ofZ/Eisomers based ono-carborane-functionalized tetraphenylethene
-
Z/Eisomerism is a very important and interesting phenomenon in the field of chemistry. In many cases, people ignore the difference betweenZ/Eisomers, and most studies investigate this hybrid system, thereby limiting the precise and in-depth understanding of the structure-performance relationship of materials. At present, only a fewZ/Eisomers of TPE derivatives can be separated, and the synthesis and separation of isomers modified by carborane substituents have not been reported. In this work, twoZ/Eisomers, namely,Z-TPE-2CarandE-TPE-2Car, with clear configuration were synthesized using an effective route. Both compounds have strong aggregation-induced luminescence (AIE) activity. The solid-state emission peaks ofZ-TPE-2CarandE-TPE-2Carare 528 and 533 nm, respectively, and the emission peaks are shifted by 5 nm. The introduction of phenyl carborane substituents makes the two isomers have high solid-state fluorescence quantum yields, reaching 99% and 90%, respectively.
- Chen, Wei,Li, Xiang,Liu, Yujie,Qin, Na,Sha, Ye,Yan, Hong,Zhang, Weihua,Zhou, Qin,Zhu, Miao
-
p. 12830 - 12837
(2021/08/03)
-
- Aggregation-induced emission molecular compound, preparation method and application thereof
-
The invention discloses an aggregation-induced emission molecular compound. The aggregation-induced emission molecular compound comprises a monosubstituted tetraphenyl ethylene derivative taking tetraphenyl ethylene as a skeleton, or a heavy atom-containi
- -
-
Paragraph 0120-0123
(2021/06/26)
-
- Sodium-metal-promoted reductive 1,2-syn-diboration of alkynes with reduction-resistant trimethoxyborane
-
Reductive 1,2-diboration of alkynes has been accomplished by means of sodium dispersion in the presence of trimethoxyborane as a reduction-resistant boron electrophile. Two boron moieties can be introduced onto alkynes with excellent syn selectivity to afford the corresponding (Z)-1,2-diborylalkenes. Bis(borate) species generated in situ can be involved in one-pot Suzuki-Miyaura arylation, formal arylboration of alkynes thus being executed.
- Fukazawa, Mizuki,Ito, Shiori,Nogi, Keisuke,Takahashi, Fumiya,Yorimitsu, Hideki
-
p. 1171 - 1179
(2020/10/18)
-
- Divergent and Stereoselective Synthesis of Tetraarylethylenes from Vinylboronates
-
The synthesis of a new tetraborylethylene (TBE) is reported, and its application in the preparation of [4+0]-tetraarylethenes (TAEs) is elucidated. TAEs have widespread applications in material science and supramolecular chemistry due to their aggregation-induced emission (AIE) properties. The divergent and stereoselective synthesis of [3+1]-, [2+2]-, and [2+1+1]-TAEs via multiple couplings of vinylboronates with aryl bromides is demonstrated. These couplings feature a broad substrate scope and excellent functional group compatibility due to mild reaction conditions. Facile access to various tetraarylethenes is provided. This strategy represents an important complement to the conventional methods employed for the synthesis of TAEs, and would be a valuable tool for synthesizing TAE-based molecules useful in functional materials, biological imaging and chemical sensing.
- Stang, Peter J.,Yao, Yisen,Zhang, Minghao,Zhao, Wanxiang
-
supporting information
p. 20090 - 20098
(2020/09/02)
-
- Simultaneous expansion of 9,10 boron-doped anthracene in longitudinal and lateral directions
-
Doubly boron-doped anthracenes and pentacenes have been longitudinally and laterally expanded through annulation of thiophene or benzene rings. The obtained series of closely related compounds allowed an assessment of key structure-property relationships with a focus on optoelectronic characteristics. Most of the products are benchtop-stable blue emitters and capable of accepting two electrons in a reversible manner. The syntheses involved late-stage modifications through photocyclization or stepwise oxidative C-C coupling (DDQ/BF3·Et2O) as well as cyclocondensation of ortho-disilylated or -diborylated aryl building blocks.
- John, Alexandra,Kirschner, Sven,Fengel, Melina K.,Bolte, Michael,Lerner, Hans-Wolfram,Wagner, Matthias
-
p. 1871 - 1877
(2019/02/28)
-
- Hydroboration and Diboration of Internal Alkynes Catalyzed by a Well-Defined Low-Valent Cobalt Catalyst
-
The use of a simple well-defined low-valent cobalt(I) catalyst [HCo(PMe 3) 4 ] capable of performing the regio- and stereoselective hydroboration of internal alkynes is reported. Extension to the diboration of internal alkynes is also related using the same reaction conditions.
- Ferrand, Laura,Lyu, Ye,Rivera-Hernández, Alejandro,Fallon, Brendan J.,Amatore, Muriel,Aubert, Corinne,Petit, Marc
-
supporting information
p. 3895 - 3904
(2017/08/29)
-
- Gold-nanoparticle-catalyzed mild diboration and indirect silaboration of alkynes without the use of silylboranes
-
Commercially available Au nanoparticles supported on TiO2 were used to catalyze the cis diboration of terminal and internal alkynes with bis(pinacolato)diboron. The products were obtained in excellent yields by using milder conditions, shorter reaction times, and lower catalyst loadings than those required for a heterogeneous Au nanopore catalyst. The catalytic system could be recovered and reused for five consecutive runs without any loss of activity. The combination of bis(pinacolato)- diboron with the 1,2-disilane in the presence of Au/TiO2 allowed for the σ-bond metathesis to take place and the in situ formation of the Au nanoparticle-tethered silylborane. Given that the Au-catalyzed silaboration of alkynes is faster than the rates of the corresponding disilylation and diboration pathways, we were able to achieve the indirect silaboration of alkynes with good chemoselectivities (65–85 %) without the direct use of silylboranes, which are expensive and difficult to synthesize.
- Kidonakis, Marios,Stratakis, Manolis
-
p. 4265 - 4271
(2017/11/09)
-
- C-H borylation by platinum catalysis
-
Herein, we describe the platinum-catalyzed borylation of aromatic C-H bonds. N-Heterocyclic carbene-ligated platinum catalysts are found to be efficient catalysts for the borylation of aromatic C(sp2)-H bonds when bis(pinacolato)diboron is used as the boron source. The most remarkable feature of these Pt catalysts is their lack of sensitivity towards the degree of steric hindrance around the C-H bonds undergoing the borylation reaction. These Pt catalysts allow for the synthesis of sterically congested 2,6-disubstituted phenylboronic esters, which are otherwise difficult to synthesize using existing C-H borylation methods. Furthermore, platinum catalysis allows for the site-selective borylation of the C-H bonds ortho to fluorine substituents in fluoroarene systems. Preliminary mechanistic studies and work towards the synthetic application of this platinum catalyzed C-H borylation process are described.
- Furukawa, Takayuki,Tobisu, Mamoru,Chatani, Naoto
-
supporting information
p. 332 - 342
(2017/05/09)
-
- New synthetic approaches towards analogues of bedaquiline
-
Multi-drug resistant tuberculosis (MDR-TB) is of growing global concern and threatens to undermine increasing efforts to control the worldwide spread of tuberculosis (TB). Bedaquiline has recently emerged as a new drug developed to specifically treat MDR-
- Priebbenow, Daniel L.,Barbaro, Lisa,Baell, Jonathan B.
-
supporting information
p. 9622 - 9628
(2016/10/25)
-
- Boronate ester post-functionalization of PPEs: versatile building blocks for poly(2,2′-(1-(4-(1,2-di(thiophen-2-yl)vinyl)phenyl)-2-(2,5-dioctylphenyl)ethene-1,2-diyl)dithiophene) and application in field effect transistors
-
A convenient and scalable strategy for post-functionalization of poly(phenylene-ethynylene)s and phenylene-ethynylene arrays from boronate ester derivatives using the thienyl group as an example. Furthermore, poly(2,2′-(1-(4-(1,2-di(thiophen-2-yl)vinyl)phenyl)-2-(2,5-dioctylphenyl)ethene-1,2-diyl)dithiophene) showed good field-effect transistor performance with an excellent mobility up to 0.723 cm2 V-1 s-1 and an on-off ratio of 104.
- Yang, Junwei,Chen, Moyun,Ma, Ji,Huang, Wei,Zhu, Haoyun,Huang, Yuli,Wang, Weizhi
-
supporting information
p. 10074 - 10078
(2015/10/12)
-
- Iron-catalyzed diboration and carboboration of alkynes
-
An iron-catalyzed diboration reaction of alkynes with bis(pinacolato)diboron (B2pin2) and external borating agents (MeOB(OR)2) affords diverse symmetrical or unsymmetrical cis-1,2-diborylalkenes. The simple protocol for th
- Nakagawa, Naohisa,Hatakeyama, Takuji,Nakamura, Masaharu
-
supporting information
p. 4257 - 4261
(2015/03/14)
-
- Solvent-and ligand-free diboration of alkynes and alkenes catalyzed by platinum nanoparticles on titania
-
Platinum nanoparticles supported on titania efficiently catalyzed the diboration of alkynes and alkenes under solvent-and ligand-free conditions in air. The cis-1,2-diborylalkenes and 1,2-diborylalkanes were obtained in moderate to excellent yields following, in most cases, a simple filtration workup protocol. The versatility of the cis-1,2-diboronvinyl compounds was demonstrated in a series of organic transformations, including the Suzuki-Miyaura cross coupling and the boron-halogen exchange. Click diboration: The diboration of alkynes and alkenes catalyzed by platinum nanoparticles on titania is shown to take place under solvent-and ligand-free conditions in air. The 1,2-diboronvinyl compounds are obtained with exclusive cis stereochemistry and are subjected to different useful chemical transformations.
- Alonso, Francisco,Moglie, Yanina,Pastor-Perez, Laura,Sepulveda-Escribano, Antonio
-
p. 857 - 865
(2014/03/21)
-
- Copper-catalyzed borylation reactions of alkynes and arynes
-
One, two, three, four: A copper(I)-phosphine complex catalyzes the diborylation of alkynes and arynes, and the tri- or tetraborylation of propargyl ethers (see scheme; pin=pinacolato). In the latter cases, the C-O bond(s) as well as the C≡C bond are borylated in one pot. Furthermore, a diborylation product serves as an intermediate in the efficient synthesis of ortho-terphenyls with pharmacological activity.
- Yoshida, Hiroto,Kawashima, Shota,Takemoto, Yuki,Okada, Kengo,Ohshita, Joji,Takaki, Ken
-
supporting information; experimental part
p. 235 - 238
(2012/02/16)
-
- Halodeboronation of organotrifluoroborates using tetrabutylammonium tribromide or cesium triiodide
-
Halodeboronation of organotrifluoroborates using commercially available tetrabutylammonium tribromide (TBATB) or cesium triiodide in aqueous medium is reported. The mild, transition metal-free method has proven to be tolerant of a wide range of functional groups. High regio- and chemoselectivity are observed. Two synthetic routes to (Z)-dibromoalkenes from alkynes, through stereodefined (Z)-2-bromoalkenyltrifluoroborates and (Z)-1,2-bis(boryl) alkenyltrifluoroborates, have been developed using the TBATB mediated bromodeboronation as the key step.
- Yao, Min-Liang,Kabalka, George W.,Blevins, David W.,Reddy, Marepally Srinivasa,Yong, Li
-
experimental part
p. 3738 - 3743
(2012/06/30)
-
- Stereoselective single (copper) or double (platinum) boronation of alkynes catalyzed by magnesia-supported copper oxide or platinum nanoparticles
-
Copper(II) oxide nanoparticles supported on magnesia have been prepared from CuII supported on magnesia by hydrogen reduction at 400°C followed by storage under ambient conditions. X-ray photoelectron spectroscopy of the material clearly shows that immediately after the reduction copper(0)-metal nanoparticles are present on the magnesia support, but they undergo fast oxidation to copper oxide upon contact with the ambient for a short time. TEM images show that the catalytically active CuO/MgO material is formed of well-dispersed copper oxide nanoparticles supported on fibrous MgO. CuO/MgO exhibits a remarkable catalytic activity for the monoborylation of aromatic, aliphatic, terminal, and internal alkynes, the products being formed with high regio-(borylation at the less substituted carbon) and stereoselectivity (trans-configured). CuO/MgO exhibits complete chemoselectivity towards the monoborylation of alkynes in the presence of alkenes. Other metal nanoparticles such as gold or palladium are inactive towards borylation, but undergo undesirable oligomerization or partial hydrogenation of the Ci£C triple bond. In contrast, platinum, either supported on magnesia or on nanoparticulate ceria, efficiently promotes the stereoselective diborylation of alkynes to yield a cis-configured diboronate alkene. By using platinum as the catalyst we have developed a tandem diborylation/hydrogenation reaction that gives vic-diboronated alkanes from alkynes in one pot.
- Grirrane, Abdessamad,Corma, Avelino,Garcia, Hermenegildo
-
scheme or table
p. 2467 - 2478
(2011/04/24)
-
- Palladium-catalyzed double cross-coupling reaction of 1,2- bis(pinacolatoboryl)alkenes and -arenes with 2,2′-dibromobiaryls: Annulative approach to functionalized polycyclic aromatic hydrocarbons
-
This study demonstrates that the double cross-coupling reaction of 1,2-bis(pinacolatoboryl)alkenes and -arenes with 2,2′-dibromobiaryls proceeds smoothly with the aid of a catalytic amount of Pd(PPh3) 4 in the presence of excess base to give a variety of polycyclic aromatic hydrocarbons, such as phenanthrenes, [5]helicene, dithienobenzenes, triphenylenes, dibenzo[g,p]chrysenes, and triphenyleno[1,2-b:4,3-b′] dithiophenes in good to high yields. It is noteworthy that the annulations using 2,2′-dibromooctafluorobiphenyl as an electrophile furnish the otherwise difficult to synthesize octafluorophenanthrenes and semi-fluorinated dibenzo[g,p]chrysenes in high yields.
- Shimizu, Masaki,Nagao, Ikuhiro,Tomioka, Yosuke,Kadowaki, Tsugumi,Hiyama, Tamejiro
-
experimental part
p. 8014 - 8026
(2011/11/05)
-
- Microwave-assisted one-pot diboration/Suzuki cross-couplings. A rapid route to tetrasubstituted alkenes
-
Internal and terminal alkynes undergo rapid platinum(0)-catalyzed diboration with bis(pinacolato)diboron in dioxane to yield cis-1,2-bis(boryl)alkenes under sealed vessel microwave conditions. Subsequent addition of aryl bromides, base and a palladium catalyst to the reaction vial followed by resubjection to microwave conditions provides tetrasubstituted ethylenes in high yields via Suzuki cross-coupling of the boron intermediates.
- Prokopcová, Hana,Ramírez, Jesús,Fernández, Elena,Kappe, C. Oliver
-
p. 4831 - 4835
(2008/09/21)
-
- Catalytic diboration of unsaturated molecules with platinum(0)-NHC: Selective synthesis of 1,2-dihydroxysulfones
-
Readily available N-heterocyclic platinum complexes provide active catalytic species for 1,2-diboration and anticipate a wide range of applications in alkenes and alkynes. Unprecedented catalytic B - B addition of heteroatom-containing sub-strates provided high selectivity into organosulfur - diboronate esters. Their in situ basic oxidation afforded the desired 1,2-dihydroxysulfones in high yields.
- Lillo, Vanesa,Mata, Jose,Ramirez, Jesus,Peris, Eduardo,Fernandez, Elena
-
p. 5829 - 5831
(2008/10/09)
-
- Convenient synthesis of α,α-difluorinated carbonyl compounds from alkynes through a fluoro-deboronation process
-
Catalytic diboration of alkynes towards alkenyl diboronates provides suitable intermediates that can be converted into α-fluorinated and α,α-difluorinated carbonyl compounds via electrophilic fluorination with Selectfluor. Georg Thieme Verlag Stuttgart.
- Ramirez, Jesus,Fernandez, Elena
-
p. 1698 - 1700
(2007/10/03)
-
- Organoboron derivatives and process for coupling organic compounds
-
This invention relates to a process for covalently coupling organic compounds which comprises: reacting an olefinic compound having at least one carbon to carbon double bond or an acetylenic compound having at least one carbon to carbon triple bond with a diboron derivative in the presence of a Group 8-11 metal catalyst to form an organoboron intermediate having an organoboronate residue on at least one carbon atom of the respective double or triple bond; and reacting the organoboron intermediate with an organic compound having a halogen or halogen-like substituent at a coupling position in the presence of a Group 8-11 metal catalyst and a suitable base, whereby the olefinic or acetylenic compound is coupled to the organic compound via a direct bond between the carbon atom having the organoboronate residue and the coupling posiitijno. This invention also relates to a process for preparing an organoboron derivative which comprises reacting an olefinic compound having a leaving group in at the allylic position with a diboron derivative in the presence of a Group 8-11 metal catalyst such that the leaving gruop is replaced with an organoboronate residue. The invention further relates to organoborn intermediates and their preparation.
- -
-
-
- Synthesis and characterization of platinum(II)-Bis(boryl) catalyst precursors for diboration of alkynes and diynes: Molecular structures of cis-[(PPh3)2Pt(B-4-Butcat)2], cis-[(PPh3)2Pt(Bcat)2], cis-[(dppe)Pt(Bcat)2], cis-[(dppb)Pt(Bcat)2]
-
The reactions of the B-B-bonded compounds B2(cat)2 (cat = 1,2-O2C6H4) (1a), B2(4-But-cat)2 (1b), and B2(OCMe2CMe2O)2 (1c) with the Pt(0)-bis(phosphine) complex [(PPh3)2Pt(η-C2H4)] (4) via oxidative addition of the B-B bond yield cis-bis(boryl) Pt(II) complexes. The molecular structures of cis-[(PPh3)2Pt(Bcat)2]·C 6D6 (3a) and cis-[(PPh3)2Pt(B-4-Butcat)2] (3b) were determined by single-crystal X-ray diffraction. Reaction of 3a with 1 equiv of the bidentate phosphine dppe (Ph2PCH2CH2PPh2) or dppb (Ph2P(CH2)4PPh2) proceeds smoothly in toluene to give cis-[(dppe)Pt(Bcat)2] (5a) and cis-[(dppb)Pt(Bcat)2] (5b), respectively, which have also been characterized by X-ray diffraction. Compounds 3a,b and 4 are highly active catalyst precursors for the diboration of alkynes and 1,3-diynes. X-ray crystal structures of (E)-(4-MeOC6H4)C(Bcat)=CH(Bcat) (10c), (Z)-(C6H5)C(Bcat)=C(C6H5)(Bcat) (10e), and (Z,Z)-(4-MeOC6H4)C(Bcat)=C(Bcat)C(Bcat)=C(4-MeOC 6H4)(Bcat) (14a) confirm the cis stereochemistry of the boron substituents in three representative cases, namely, products of the catalyzed diboration of the terminal alkyne 4-MeOC6H4C=CH, the internal alkyne PhC=CPh, and the tetraboration of the diyne 4,4′-MeOC6H4C=CC=CC6H4OMe. The presence of the C=CSiMe3 moiety in catalytic reactions gives rise to additional products other than those derived from the diboration of the alkyne group. Metathetical reactions involving the diboron reagent and products derived from C-Si bond cleavage give rise to novel tris(boronate esters) as a result of the subsequent diboration of the C=CB(OR2) moieties formed by this competing process. The absence of catalytic activity using compound 5a, the extremely low activity of 5b, and the strong decrease in activity of 3b in the presence of added PPh3 suggests that phosphine dissociation is a critical step in the catalytic pathway.
- Lesley, Gerry,Nguyen, Paul,Taylor, Nicholas J.,Marder, Todd B.,Scott, Andrew J.,Clegg, William,Norman, Nicholas C.
-
p. 5137 - 5154
(2008/10/08)
-