Borane-protected cyanides as surrogates of h-bonded cyanides in [FeFe]-hydrogenase active site models

Brian C. Manor; Mark R. Ringenberg; Thomas B. Rauchfuss

doi:10.1021/ic500470z

Borane-protected cyanides as surrogates of h-bonded cyanides in [FeFe]-hydrogenase active site models

Brian C. Manor, Mark R. Ringenberg, Thomas B. Rauchfuss

Chemistry

Research output: Contribution to journal › Article › peer-review

Abstract

Triarylborane Lewis acids bind [Fe₂(pdt)(CO)₄(CN) ₂]^2- [1]^2- (pdt^2- = 1,3-propanedithiolate) and [Fe₂(adt)(CO)₄(CN) ₂]^2- [3]^2- (adt^2- = 1,3-azadithiolate, HN(CH₂S^-)₂) to give the 2:1 adducts [Fe₂(xdt)(CO)₄(CNBAr₃) ₂]^2-. Attempts to prepare the 1:1 adducts [1(BAr ₃)]^2- (Ar = Ph, C₆F₅) were unsuccessful, but related 1:1 adducts were obtained using the bulky borane B(C₆F₄-o-C₆F₅)₃ (BAr ^F₃). By virtue of the N-protection by the borane, salts of [Fe₂(pdt)(CO)₄(CNBAr₃)₂] ^2- sustain protonation to give hydrides that are stable (in contrast to [H1]^-). The hydrides [H1(BAr₃)₂]^- are 2.5-5 pK_a units more acidic than the parent [H1]^-. The adducts [1(BAr₃)₂]^2- oxidize quasi-reversibly around -0.3 V versus Fc^0/+ in contrast to ca. -0.8 V observed for the [1]^2-/- couple. A simplified synthesis of [1] ^2-, [3]^2-, and [Fe₂(pdt)(CO) ₅(CN)]^- ([2]^-) was developed, entailing reaction of the diiron hexacarbonyl complexes with KCN in MeCN.

Original language	English (US)
Pages (from-to)	7241-7247
Number of pages	7
Journal	Inorganic Chemistry
Volume	53
Issue number	14
DOIs	https://doi.org/10.1021/ic500470z
State	Published - Jul 21 2014

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Physical and Theoretical Chemistry
Inorganic Chemistry

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10.1021/ic500470z

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title = "Borane-protected cyanides as surrogates of h-bonded cyanides in [FeFe]-hydrogenase active site models",

abstract = "Triarylborane Lewis acids bind [Fe2(pdt)(CO)4(CN) 2]2- [1]2- (pdt2- = 1,3-propanedithiolate) and [Fe2(adt)(CO)4(CN) 2]2- [3]2- (adt2- = 1,3-azadithiolate, HN(CH2S-)2) to give the 2:1 adducts [Fe2(xdt)(CO)4(CNBAr3) 2]2-. Attempts to prepare the 1:1 adducts [1(BAr 3)]2- (Ar = Ph, C6F5) were unsuccessful, but related 1:1 adducts were obtained using the bulky borane B(C6F4-o-C6F5)3 (BAr F3). By virtue of the N-protection by the borane, salts of [Fe2(pdt)(CO)4(CNBAr3)2] 2- sustain protonation to give hydrides that are stable (in contrast to [H1]-). The hydrides [H1(BAr3)2]- are 2.5-5 pKa units more acidic than the parent [H1]-. The adducts [1(BAr3)2]2- oxidize quasi-reversibly around -0.3 V versus Fc0/+ in contrast to ca. -0.8 V observed for the [1]2-/- couple. A simplified synthesis of [1] 2-, [3]2-, and [Fe2(pdt)(CO) 5(CN)]- ([2]-) was developed, entailing reaction of the diiron hexacarbonyl complexes with KCN in MeCN.",

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AU - Manor, Brian C.

AU - Ringenberg, Mark R.

AU - Rauchfuss, Thomas B.

PY - 2014/7/21

Y1 - 2014/7/21

N2 - Triarylborane Lewis acids bind [Fe2(pdt)(CO)4(CN) 2]2- [1]2- (pdt2- = 1,3-propanedithiolate) and [Fe2(adt)(CO)4(CN) 2]2- [3]2- (adt2- = 1,3-azadithiolate, HN(CH2S-)2) to give the 2:1 adducts [Fe2(xdt)(CO)4(CNBAr3) 2]2-. Attempts to prepare the 1:1 adducts [1(BAr 3)]2- (Ar = Ph, C6F5) were unsuccessful, but related 1:1 adducts were obtained using the bulky borane B(C6F4-o-C6F5)3 (BAr F3). By virtue of the N-protection by the borane, salts of [Fe2(pdt)(CO)4(CNBAr3)2] 2- sustain protonation to give hydrides that are stable (in contrast to [H1]-). The hydrides [H1(BAr3)2]- are 2.5-5 pKa units more acidic than the parent [H1]-. The adducts [1(BAr3)2]2- oxidize quasi-reversibly around -0.3 V versus Fc0/+ in contrast to ca. -0.8 V observed for the [1]2-/- couple. A simplified synthesis of [1] 2-, [3]2-, and [Fe2(pdt)(CO) 5(CN)]- ([2]-) was developed, entailing reaction of the diiron hexacarbonyl complexes with KCN in MeCN.

AB - Triarylborane Lewis acids bind [Fe2(pdt)(CO)4(CN) 2]2- [1]2- (pdt2- = 1,3-propanedithiolate) and [Fe2(adt)(CO)4(CN) 2]2- [3]2- (adt2- = 1,3-azadithiolate, HN(CH2S-)2) to give the 2:1 adducts [Fe2(xdt)(CO)4(CNBAr3) 2]2-. Attempts to prepare the 1:1 adducts [1(BAr 3)]2- (Ar = Ph, C6F5) were unsuccessful, but related 1:1 adducts were obtained using the bulky borane B(C6F4-o-C6F5)3 (BAr F3). By virtue of the N-protection by the borane, salts of [Fe2(pdt)(CO)4(CNBAr3)2] 2- sustain protonation to give hydrides that are stable (in contrast to [H1]-). The hydrides [H1(BAr3)2]- are 2.5-5 pKa units more acidic than the parent [H1]-. The adducts [1(BAr3)2]2- oxidize quasi-reversibly around -0.3 V versus Fc0/+ in contrast to ca. -0.8 V observed for the [1]2-/- couple. A simplified synthesis of [1] 2-, [3]2-, and [Fe2(pdt)(CO) 5(CN)]- ([2]-) was developed, entailing reaction of the diiron hexacarbonyl complexes with KCN in MeCN.

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JO - Inorganic Chemistry

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ER -

Borane-protected cyanides as surrogates of h-bonded cyanides in [FeFe]-hydrogenase active site models

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