Boratropic rearrangements in tris(pyrazolyl)borate molybdenum mononitrosyl complexes: effects of co-ligands

Cano, Mercedes; Heras, J.V.; Monge, Ángeles; Pinilla, Elena; Santamaria, Elena; Hinton, Helen A.; Jones, Christopher J.; McCleverty, Jon A.

doi:10.1039/dt9950002281

Cited by 11 publications

(8 citation statements)

References 16 publications

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“…22 Thus, it would appear that the presence of methyl groups in the 5-position, ostensibly useful to protect the boron atom from attack, might, in fact, serve to destabilize the ligand by maximizing the steric crowding around it. 30,31 Because hydrolysis of Tp ligands occurs readily at low pH in aqueous solution, direct protonation initially appears to offer a possible mechanism to account for the observed degradation. However, several lines of evidence militate against this hypothesis.…”

Section: Resultsmentioning

confidence: 99%

“…Ligand rearrangements, believed to involve either 1,2-borotropic or 1,2-metallatropic shifts, have been observed for a number of ligands of intermediate steric demand. [29][30][31][32][33][34] More problematic has been the observation of partial and even complete degradation of such ligands within the coordination sphere of metals. Such reactions have been described both for maingroup metal complexes [35][36][37][38] and for transition metals.…”

Section: Introductionmentioning

confidence: 99%

“…Insertion of formaldehyde and CO 2 into the B−H bond of Bp ligands and hydroboration of acyl and iminoacyl complexes of molybdenum lead to the formation of heteroscorpionate ligands. Ligand rearrangements, believed to involve either 1,2-borotropic or 1,2-metallatropic shifts, have been observed for a number of ligands of intermediate steric demand. − More problematic has been the observation of partial and even complete degradation of such ligands within the coordination sphere of metals. Such reactions have been described both for main-group metal complexes − and for transition metals. − This propensity to decomposition has become particularly manifest for the Tp Me2 ligand bound to lanthanide centers.…”

Section: Introductionmentioning

confidence: 99%

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Facile Pyrazolylborate Ligand Degradation at Lanthanide Centers: X-ray Crystal Structures of Pyrazolylborinate-Bridged Bimetallics

et al. 2002

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Adventitious hydrolysis of a number of different complexes with the molecular formula Ln(Tp(Me2))(2)X [Tp(Me2) = (HB(dmpz)(3)), where X is a basic anionic ligand] in various solvents, yielded crystals of highly insoluble dimers of the general formula [Ln(Tp(Me2))(mu-BOp(Me2))](2) (1) [Ln = La, Ce, Sm; BOp(Me2) = (HBO(dmpz)(2))(2)(-); dmpzH = 3,5-dimethylpyrazole]. The results of several single-crystal X-ray determinations are reported. One metal nitrogen distance, that lying across from the two negatively charged bridging oxygen atoms, is 0.06 A longer than the others, suggesting an unusual trans influence at a lanthanide center. The formation of 1 is proposed to involve the intermediacy of Ln(Tp(Me2))(2)OH formed by protonolysis with adventitious water.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Facile Pyrazolylborate Ligand Degradation at Lanthanide Centers: X-ray Crystal Structures of Pyrazolylborinate-Bridged Bimetallics

et al. 2002

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“…26 A number of ML* 2 (M ) Fe II , Co II , Ni II ) complexes have been reported by Trofimenko et al 25 and related ligands have been observed to undergo 1,2-boratropic rearrangements. [39][40][41] The observation of a novel "side-on" bonded pyrazole unit in L 2 U III I provides an insight into how rearrangements of this type may be facilitated. 42 The relative rates of formation of L*MoO(S 2 PR 2 ) and LMoO(S 2 PR 2 ) complexes (minutes versus hours, respectively) may also reflect the capacity of the ligands to reduce steric interactions, especially in the transition states involved.…”

Section: Resultsmentioning

confidence: 99%

Oxygen Atom Transfer, Sulfur Atom Transfer, and Correlated Electron−Nucleophile Transfer Reactions of Oxo- and Thiomolybdenum(IV) Complexes: Synthesis of Oxothiomolybdenum(VI) and (Hydroxo)oxomolybdenum(V) Species

et al. 1996

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Reaction of Mo IV O(S 2 PR 2 ) 2 with K{HB(Pr i pz) 3 } [HB(Pr i pz) 3 -) hydrotris(isopropylpyrazol-1-yl)borate] in refluxing toluene affords green L*Mo IV O(S 2 PR 2 -S,S′) complexes [L* ) HB(3-Pr i pz) 2 (5-Pr i pz) -) hydrobis(3-isopropylpyrazol-1-yl)(5-isopropylpyrazol-1-yl)borate; R ) Pr i , Ph], which are converted upon reaction with boron sulfide in dichloromethane to the yellow thio analogues L*Mo IV S(S 2 PR 2 -S,S′). Crystals of L*Mo IV O(S 2 PPr i 2 ) are monoclinic, space group P2 1 /n, with a ) 10.024 (2) Å, b ) 20.999(9) Å, c ) 15.368(5) Å, ) 100.57(2)°, V ) 3180(2) Å 3 , and Z ) 4. Crystals of L*Mo IV S(S 2 PPh 2 ) are monoclinic, space group P2 1 , with a ) 10.801(8) Å, b ) 13.100(5) Å, c ) 12.023(9) Å, ) 99.56(10)°, V ) 1678(2) Å 3 , and Z ) 2. The mononuclear, distortedoctahedral complexes are isostructural and are composed of a terminal chalcogenide ligand [ModO ) 1.671(3) Å, ModS ) 2.126(3) Å], a bidentate dithiophosphinate-S,S′ ligand, and a facial, tridentate L* ligand. In both cases the 5-isopropylpyrazole group is bound trans to the ModE group (E ) O, S). Oxygen atom transfer to L*Mo IV S(S 2 PR 2 ) and sulfur atom transfer to L*Mo IV O(S 2 PR 2 ) produce the oxo-thio-Mo(VI) complexes L*Mo VI -OS(S 2 PR 2 -S). NOESY experiments confirm that the 5-isopropylpyrazole group is trans to the ModO group in these chiral complexes. Ferrocenium oxidation of L*Mo IV E(S 2 PR 2 ) yields the corresponding oxo-and thioMo(V) complexes [L*Mo V E(S 2 PR 2 -S,S′)] + , respectively; the [L*Mo V O(S 2 PR 2 -S,S′)] + complexes react with water to produce (hydroxo)oxo-Mo(V) species, L*Mo V O(OH)(S 2 PR 2 -S), while the thio analogues are decomposed by water. The complex L′Mo V OCl 2 [L′ ) HB(3-Pr i pz) 3 -) hydrotris(3-isopropylpyrazol-1-yl)borate] was prepared by reacting L′Mo VI O 2 Cl with PPh 3 in dichloromethane; this complex does not react with sulfiding agents to produce the analogous thio complex. IntroductionThe simple replacement of a terminal oxo ligand by a terminal thio 2 ligand is a reaction plagued by practical limitations; the facile reduction of high-valent metal centers by sulfide and the formation of polynuclear µ-thio complexes usually conspire to prevent clean reactions. Nevertheless, this reaction has played a vital role in the generation of [Mo VI OS] 2+ , [Mo V -OS] + and [Mo V O(SH)] 2+ complexes, some of which are important models for the molybdenum centers formed during turnover of xanthine oxidase and xanthine dehydrogenase. [3][4][5] Most oxo-thio-Mo(VI) complexes have been produced by sulfidation of oxo complexes; examples include the oxothiomolybdates, [Mo VI O 4-n S n ] 2-, 6 the Wieghardt complexes Mo VI -OS(ONR 2 ) 2 , 7 and the organometallic species (η 5 -C 5 Me 5 )Mo VI -OS(CH 2 SiMe 3 ). 8 Generally, however, sulfidation of oxoMo(VI) complexes does not lead to clean replacement of an

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“…asymmetric into the symmetric form have been observed in several complexes containing some of these ligands, [9][10][11] although, in a previous paper, the opposite rearrangement has also been observed in complexes containing the Tp 3Pr i ,5Me ligand. 12 In contrast to the well established behaviour of the tris-(pyrazolyl)borate ligands, no related steric requirements have been described for the tetrakis(pyrazolyl)borates, [B(pz R ) 4 ] Ϫ , although the molecular structures of some of their complexes have revealed the symmetric (3R,3R,3R,3R) form in all cases. 11,13- 16 However there is no evidence of regiospecific co-ordination of these ligands.…”

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confidence: 99%

Chemistry of bulky tetrakis(pyrazolyl)borate ligands [B(pzR)4]− (R = p-CH3OC6H4 or C6H11) †

Campo¹,

Cano²,

Heras³

et al. 1998

J. Chem. Soc., Dalton Trans.

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Boratropic rearrangements in tris(pyrazolyl)borate molybdenum mononitrosyl complexes: effects of co-ligands

Cited by 11 publications

References 16 publications

Facile Pyrazolylborate Ligand Degradation at Lanthanide Centers: X-ray Crystal Structures of Pyrazolylborinate-Bridged Bimetallics

Facile Pyrazolylborate Ligand Degradation at Lanthanide Centers: X-ray Crystal Structures of Pyrazolylborinate-Bridged Bimetallics

Oxygen Atom Transfer, Sulfur Atom Transfer, and Correlated Electron−Nucleophile Transfer Reactions of Oxo- and Thiomolybdenum(IV) Complexes: Synthesis of Oxothiomolybdenum(VI) and (Hydroxo)oxomolybdenum(V) Species

Chemistry of bulky tetrakis(pyrazolyl)borate ligands [B(pzR)4]− (R = p-CH3OC6H4 or C6H11) †

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