catecholborane
{{chembox
|Watchedfields = changed
|verifiedrevid = 427312003
|Name = Catecholborane
|ImageFile = Catecholborane structure.png
|ImageFile1 = Catecholborane-3D-spacefill.png
|ImageAlt1 = Catecholborane molecule
|PIN = 2H-1,3,2-Benzodioxaborole
|OtherNames = 7,9-dioxa-8λ2-borabicyclo[4.3.0]nona-1,3,5-triene
|Section1={{Chembox Identifiers
|SMILES = [B]1OC2=CC=CC=C2O1
|ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
|ChemSpiderID = 10617125
|InChI = 1/C6H5BO2/c1-2-4-6-5(3-1)8-7-9-6/h1-4,7H
|InChIKey = CENMEJUYOOMFFZ-UHFFFAOYAI
|SMILES1 = c1cccc2OBOc12
|StdInChI_Ref = {{stdinchicite|correct|chemspider}}
|StdInChI = 1S/C6H5BO2/c1-2-4-6-5(3-1)8-7-9-6/h1-4,7H
|StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
|StdInChIKey = CENMEJUYOOMFFZ-UHFFFAOYSA-N
|CASNo_Ref = {{cascite|correct|??}}
|CASNo = 274-07-7
|UNII_Ref = {{fdacite|correct|FDA}}
|UNII = UB69382H5J
|PubChem = 6327445
|EC_number = 205-991-5
}}
|Section2={{Chembox Properties
|Formula = C6H5BO2
|MolarMass = 119.92 g/mol
|Appearance = Colorless liquid
|Density = 1.125 g/cm3, liquid
|MeltingPtC = 12
|BoilingPtC = 50
|BoilingPt_notes = at 50 mmHg
}}
|Section7={{Chembox Hazards
|NFPA-H = 1 | NFPA-F = 4 | NFPA-R = 2 | NFPA-S = W
|GHSPictograms = {{GHS02}}{{GHS05}}
|GHSSignalWord = Danger
|HPhrases = {{H-phrases|225|314}}
|PPhrases = {{P-phrases|210|233|240|241|242|243|260|264|280|301+330+331|303+361+353|304+340|305+351+338|310|321|363|370+378|403+235|405|501}}
|FlashPtC = 2
}}
}}
Catecholborane (abbreviated HBcat) is an organoboron compound that is useful in organic synthesis. This colourless liquid is a derivative of catechol and a borane, having the formula C6H4O2BH.
Synthesis and structure
Traditionally catecholborane is produced by treating catechol with borane (BH3) in a cooled solution of THF. However, this method results in a loss of 2 mole equivalents of the hydride. Nöth and Männig described the reaction of alkali-metal boron hydride (LiBH4, NaBH4, KBH4) with tris(catecholato)bisborane in an ethereal solvent such as diethyl ether.[http://www.freepatentsonline.com/4739096.html Process for producing catecholborane – Patent 4739096] In 2001, Herbert Brown and coworkers prepared catecholborane by treatment of tri-o-phenylene bis-borate with diborane.{{cite journal|doi=10.1021/op000291w|title=New Economical, Convenient Procedures for the Synthesis of Catecholborane|year=2000|last1=Kanth|first1=Josyula V. B.|last2=Periasamy|first2=Mariappan|last3=Brown|first3=Herbert C.|journal=Organic Process Research & Development|volume=4|issue=6|pages=550–553}}
Unlike borane itself or alkylboranes, catechol borane exists as a monomer. This behavior is a consequence of the electronic influence of the aryloxy groups that diminish the Lewis acidity of the boron centre. Pinacolborane adopts a similar structure.
Reactions
Catecholborane is less reactive in hydroborations than borane-THF or borane-dimethylsulfide.
When catecholborane is treated with a terminal alkyne, a trans vinylborane is formed:
:C6H4O2BH + HC2R → C6H4O2B-CHCHR
The product is a precursor to the Suzuki reaction and is the only borane which stops at the alkene instead of reacting further to the alkane. Janice Gorzynski Smith, Organic Chemistry: Second Ed. 2008. pp 1007{{OrgSynth|author1-link=Norio Miyaura|author2-link=Akira Suzuki (chemist)|first1=Norio|last1=Miyaura|first2=Akira|last2=Suzuki| year = 1990|title=Palladium-Catalyzed Reaction of 1-Alkenylboronates with Vinylic Halides: (1Z,3E)-1-Phenyl-1,3-octadiene|volume=68|page= 130|doi=10.15227/orgsyn.068.0130}}
Catecholborane may be used as a stereoselective reducing agent when converting β-hydroxy ketones to syn 1,3-diols.
Catecholborane oxidatively adds to low valent metal complexes, affording boryl complexes.{{cite journal |doi=10.1021/acs.chemrev.6b00193|title=Diboron(4) Compounds: From Structural Curiosity to Synthetic Workhorse|year=2016|last1=Neeve|first1=Emily C.|last2=Geier|first2=Stephen J.|last3=Mkhalid|first3=Ibraheem A. I.|last4=Westcott|first4=Stephen A.|last5=Marder|first5=Todd B.|journal=Chemical Reviews|volume=116|issue=16|pages=9091–9161|pmid=27434758|doi-access=free|hdl=1807/78811|hdl-access=free}}
:C6H4O2BH + Pt(PR3)2 → (C6H4O2B)Pt(PR3)2H