Porphyrin complexes containing coordinated BOB groups: Synthesis, chemical reactivity and the structure of [BOB(tpClpp)]2+

Warwick J. Belcher, Michael C. Hodgson, Kenji Sumida, Ana Torvisco, Karin Ruhlandt, D. C. Ware, P. D W Boyd, P. J. Brothers

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Abstract

The reactions of boron halides with free base porphyrins under conditions where partial hydrolysis of the boron halides can occur give diboron porphyrin complexes containing BOB moieties in which each boron is bonded to two porphyrin nitrogen atoms. BF3•OEt2 with H2(por) gives B2OF2(por) (por = tpp, ttp, tpClpp, oep) which has an asymmetric structure in which one boron lies in the porphyrin plane (B ip) while the other lies above it (Boop). BCl 3•MeCN with H2(por) gives B2O 2(BCl3)2(por) which contains a four-membered B2O2 ring and is stable only in the presence of excess BCl3. BBr3 with Li2(tpClpp) gives the dicationic complex [B2O(tpClpp)]2+ as its [BBr 4]- salt, and is the first example of a boron porphyrin containing three-coordinate boron to be structurally characterised. B 2O2(BCl3)2(por) can be chromatographed on basic alumina to give the hydroxyboron complex B 2O(OH)2(por), which is deduced from its NMR spectra and DFT calculations to have a structure analogous to B2OF 2(por). The OH protons are shifted upfield to near δ -4 (B oop-OH) and -10 (Bip-OH) by the diamagnetic porphyrin ring current. The reaction of either B2O2(BCl 3)2(por) or B2O(OH)2(por) (por = ttp, tpClpp) with alcohols (ROH, R = Et, 4-C6H4CH 3) gives B2O(OR)2(por), which can in turn be converted to B2O(OR)(OH)(por) by repeated chromatography. The reaction of PhBCl2 with H2(por) (por = ttp, tpClpp) gives B2O(Ph)(OH)(por) which has been characterised by spectroscopy in concert with DFT calculations. It is a further example of the B 2OF2(por) structural type, in which the phenyl group is coordinated to the out-of-plane boron and the OH group to the in-plane boron, as are its derivatives B2O(Ph)(X)(tpClpp) (X = F, OEt). Steric drivers for the facile hydrolysis of haloboron porphyrins relative to their dipyrromethene and expanded porphyrin counterparts are discussed.

Original languageEnglish (US)
Pages (from-to)1602-1614
Number of pages13
JournalDalton Transactions
Issue number12
DOIs
StatePublished - 2008

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Chemical reactivity
Boron
Porphyrins
Discrete Fourier transforms
Hydrolysis
Aluminum Oxide
Chromatography
Protons
Nitrogen
Salts
Alcohols
Nuclear magnetic resonance
Spectroscopy
Derivatives
Atoms

ASJC Scopus subject areas

  • Chemistry(all)

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Porphyrin complexes containing coordinated BOB groups : Synthesis, chemical reactivity and the structure of [BOB(tpClpp)]2+. / Belcher, Warwick J.; Hodgson, Michael C.; Sumida, Kenji; Torvisco, Ana; Ruhlandt, Karin; Ware, D. C.; Boyd, P. D W; Brothers, P. J.

In: Dalton Transactions, No. 12, 2008, p. 1602-1614.

Research output: Contribution to journalArticle

Belcher, Warwick J. ; Hodgson, Michael C. ; Sumida, Kenji ; Torvisco, Ana ; Ruhlandt, Karin ; Ware, D. C. ; Boyd, P. D W ; Brothers, P. J. / Porphyrin complexes containing coordinated BOB groups : Synthesis, chemical reactivity and the structure of [BOB(tpClpp)]2+. In: Dalton Transactions. 2008 ; No. 12. pp. 1602-1614.
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abstract = "The reactions of boron halides with free base porphyrins under conditions where partial hydrolysis of the boron halides can occur give diboron porphyrin complexes containing BOB moieties in which each boron is bonded to two porphyrin nitrogen atoms. BF3•OEt2 with H2(por) gives B2OF2(por) (por = tpp, ttp, tpClpp, oep) which has an asymmetric structure in which one boron lies in the porphyrin plane (B ip) while the other lies above it (Boop). BCl 3•MeCN with H2(por) gives B2O 2(BCl3)2(por) which contains a four-membered B2O2 ring and is stable only in the presence of excess BCl3. BBr3 with Li2(tpClpp) gives the dicationic complex [B2O(tpClpp)]2+ as its [BBr 4]- salt, and is the first example of a boron porphyrin containing three-coordinate boron to be structurally characterised. B 2O2(BCl3)2(por) can be chromatographed on basic alumina to give the hydroxyboron complex B 2O(OH)2(por), which is deduced from its NMR spectra and DFT calculations to have a structure analogous to B2OF 2(por). The OH protons are shifted upfield to near δ -4 (B oop-OH) and -10 (Bip-OH) by the diamagnetic porphyrin ring current. The reaction of either B2O2(BCl 3)2(por) or B2O(OH)2(por) (por = ttp, tpClpp) with alcohols (ROH, R = Et, 4-C6H4CH 3) gives B2O(OR)2(por), which can in turn be converted to B2O(OR)(OH)(por) by repeated chromatography. The reaction of PhBCl2 with H2(por) (por = ttp, tpClpp) gives B2O(Ph)(OH)(por) which has been characterised by spectroscopy in concert with DFT calculations. It is a further example of the B 2OF2(por) structural type, in which the phenyl group is coordinated to the out-of-plane boron and the OH group to the in-plane boron, as are its derivatives B2O(Ph)(X)(tpClpp) (X = F, OEt). Steric drivers for the facile hydrolysis of haloboron porphyrins relative to their dipyrromethene and expanded porphyrin counterparts are discussed.",
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T2 - Synthesis, chemical reactivity and the structure of [BOB(tpClpp)]2+

AU - Belcher, Warwick J.

AU - Hodgson, Michael C.

AU - Sumida, Kenji

AU - Torvisco, Ana

AU - Ruhlandt, Karin

AU - Ware, D. C.

AU - Boyd, P. D W

AU - Brothers, P. J.

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N2 - The reactions of boron halides with free base porphyrins under conditions where partial hydrolysis of the boron halides can occur give diboron porphyrin complexes containing BOB moieties in which each boron is bonded to two porphyrin nitrogen atoms. BF3•OEt2 with H2(por) gives B2OF2(por) (por = tpp, ttp, tpClpp, oep) which has an asymmetric structure in which one boron lies in the porphyrin plane (B ip) while the other lies above it (Boop). BCl 3•MeCN with H2(por) gives B2O 2(BCl3)2(por) which contains a four-membered B2O2 ring and is stable only in the presence of excess BCl3. BBr3 with Li2(tpClpp) gives the dicationic complex [B2O(tpClpp)]2+ as its [BBr 4]- salt, and is the first example of a boron porphyrin containing three-coordinate boron to be structurally characterised. B 2O2(BCl3)2(por) can be chromatographed on basic alumina to give the hydroxyboron complex B 2O(OH)2(por), which is deduced from its NMR spectra and DFT calculations to have a structure analogous to B2OF 2(por). The OH protons are shifted upfield to near δ -4 (B oop-OH) and -10 (Bip-OH) by the diamagnetic porphyrin ring current. The reaction of either B2O2(BCl 3)2(por) or B2O(OH)2(por) (por = ttp, tpClpp) with alcohols (ROH, R = Et, 4-C6H4CH 3) gives B2O(OR)2(por), which can in turn be converted to B2O(OR)(OH)(por) by repeated chromatography. The reaction of PhBCl2 with H2(por) (por = ttp, tpClpp) gives B2O(Ph)(OH)(por) which has been characterised by spectroscopy in concert with DFT calculations. It is a further example of the B 2OF2(por) structural type, in which the phenyl group is coordinated to the out-of-plane boron and the OH group to the in-plane boron, as are its derivatives B2O(Ph)(X)(tpClpp) (X = F, OEt). Steric drivers for the facile hydrolysis of haloboron porphyrins relative to their dipyrromethene and expanded porphyrin counterparts are discussed.

AB - The reactions of boron halides with free base porphyrins under conditions where partial hydrolysis of the boron halides can occur give diboron porphyrin complexes containing BOB moieties in which each boron is bonded to two porphyrin nitrogen atoms. BF3•OEt2 with H2(por) gives B2OF2(por) (por = tpp, ttp, tpClpp, oep) which has an asymmetric structure in which one boron lies in the porphyrin plane (B ip) while the other lies above it (Boop). BCl 3•MeCN with H2(por) gives B2O 2(BCl3)2(por) which contains a four-membered B2O2 ring and is stable only in the presence of excess BCl3. BBr3 with Li2(tpClpp) gives the dicationic complex [B2O(tpClpp)]2+ as its [BBr 4]- salt, and is the first example of a boron porphyrin containing three-coordinate boron to be structurally characterised. B 2O2(BCl3)2(por) can be chromatographed on basic alumina to give the hydroxyboron complex B 2O(OH)2(por), which is deduced from its NMR spectra and DFT calculations to have a structure analogous to B2OF 2(por). The OH protons are shifted upfield to near δ -4 (B oop-OH) and -10 (Bip-OH) by the diamagnetic porphyrin ring current. The reaction of either B2O2(BCl 3)2(por) or B2O(OH)2(por) (por = ttp, tpClpp) with alcohols (ROH, R = Et, 4-C6H4CH 3) gives B2O(OR)2(por), which can in turn be converted to B2O(OR)(OH)(por) by repeated chromatography. The reaction of PhBCl2 with H2(por) (por = ttp, tpClpp) gives B2O(Ph)(OH)(por) which has been characterised by spectroscopy in concert with DFT calculations. It is a further example of the B 2OF2(por) structural type, in which the phenyl group is coordinated to the out-of-plane boron and the OH group to the in-plane boron, as are its derivatives B2O(Ph)(X)(tpClpp) (X = F, OEt). Steric drivers for the facile hydrolysis of haloboron porphyrins relative to their dipyrromethene and expanded porphyrin counterparts are discussed.

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