1,4-addition of alkyl halides to a side-on bound bafnocene dinitrogen complex

David Benito-Garagorri; Wesley H. Bernskoetter; Emil Lobkovsky; Paul J. Chirik

doi:10.1021/om9004548

1,4-addition of alkyl halides to a side-on bound bafnocene dinitrogen complex

David Benito-Garagorri, Wesley H. Bernskoetter, Emil Lobkovsky, Paul J. Chirik

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Abstract

Attempts to functionalize the side-on coordinated dinitrogen ligand in [(eta; ⁵-C ₅Me ₄H) ₂Hf] ₂(μ ₂, eta; ² eta; ²-N ₂) by addition of methyl halides such as CH ₃X (X = Cl, Br, I) or alkyl halides (R-X = CH ₃CH ₂Br, CH ₃CH ₂I, and CH ₃CH ₂CH ₂C1) resulted in 1,4-addition to yield metastable, weakly activated hafnocene end-on dinitrogen complexes, [(eta; ⁵-C ₅Me ₄H) ₂HfR] (μ ₂, (eta; ¹, eta; ¹-N ₂) The product of methyl iodide addition, [(eta; ⁵-C ₅Me ₄H) ₂HfCH ₃](eta; ¹, eta; ¹-N ₂) was structurally characterized and confirmed the hapticity of the N ₂ ligand. Addition of the radical clocks 6-chloro-l-hexene and chloromethylcyclopropane also yielded 1,4-addition products with accompanying cyclization and ring-opening, respectively. In contrast, treatment of [(eta; ⁵-C ₅Me ₄H) ₂Hf] ₂-(μ ₂, η ², η ²-N ₂) with benzyl chloride, benzyl bromide, or allyl bromide yielded only small quantities of the 1,4-addition product, with the majority of the mixture being the hafnocene dihalide (η ⁵-C ₅Me ₄H) ₂HfX ₂ and organic products of radical coupling. In benzene-d ₆ solution at 23 °C, the 1,4-addition products undergo disproportionation with loss of N ₂ to yield the hafnocene alkyl halide complexes (η ⁵-C ₅Me ₄H) ₂Hf(R)X along with concomitant regeneration of the strongly activated side-on dinitrogen complex [(η ⁵-C ₅Me ₄H) ₂(μ ₂, η ², η ²-N ₂). This rearrangement is sensitive to both the halide and the alkyl substituents, where smaller groups undergo the most rapid rates of reaction, likely due to the accessibility of side-on bound N ₂ intermediates.

Original language	English (US)
Pages (from-to)	4807-4813
Number of pages	7
Journal	Organometallics
Volume	28
Issue number	16
DOIs	https://doi.org/10.1021/om9004548
State	Published - Aug 24 2009
Externally published	Yes

All Science Journal Classification (ASJC) codes

Physical and Theoretical Chemistry
Organic Chemistry
Inorganic Chemistry

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10.1021/om9004548

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@article{b8efc4568f784a7e8dd38671320af4ce,

title = "1,4-addition of alkyl halides to a side-on bound bafnocene dinitrogen complex",

abstract = "Attempts to functionalize the side-on coordinated dinitrogen ligand in [(eta; 5-C 5Me 4H) 2Hf] 2(μ 2, eta; 2 eta; 2-N 2) by addition of methyl halides such as CH 3X (X = Cl, Br, I) or alkyl halides (R-X = CH 3CH 2Br, CH 3CH 2I, and CH 3CH 2CH 2C1) resulted in 1,4-addition to yield metastable, weakly activated hafnocene end-on dinitrogen complexes, [(eta; 5-C 5Me 4H) 2HfR] (μ 2, (eta; 1, eta; 1-N 2) The product of methyl iodide addition, [(eta; 5-C 5Me 4H) 2HfCH 3](eta; 1, eta; 1-N 2) was structurally characterized and confirmed the hapticity of the N 2 ligand. Addition of the radical clocks 6-chloro-l-hexene and chloromethylcyclopropane also yielded 1,4-addition products with accompanying cyclization and ring-opening, respectively. In contrast, treatment of [(eta; 5-C 5Me 4H) 2Hf] 2-(μ 2, η 2, η 2-N 2) with benzyl chloride, benzyl bromide, or allyl bromide yielded only small quantities of the 1,4-addition product, with the majority of the mixture being the hafnocene dihalide (η 5-C 5Me 4H) 2HfX 2 and organic products of radical coupling. In benzene-d 6 solution at 23 °C, the 1,4-addition products undergo disproportionation with loss of N 2 to yield the hafnocene alkyl halide complexes (η 5-C 5Me 4H) 2Hf(R)X along with concomitant regeneration of the strongly activated side-on dinitrogen complex [(η 5-C 5Me 4H) 2(μ 2, η 2, η 2-N 2). This rearrangement is sensitive to both the halide and the alkyl substituents, where smaller groups undergo the most rapid rates of reaction, likely due to the accessibility of side-on bound N 2 intermediates.",

author = "David Benito-Garagorri and Bernskoetter, {Wesley H.} and Emil Lobkovsky and Chirik, {Paul J.}",

year = "2009",

month = aug,

day = "24",

doi = "10.1021/om9004548",

language = "English (US)",

volume = "28",

pages = "4807--4813",

journal = "Organometallics",

issn = "0276-7333",

publisher = "American Chemical Society",

number = "16",

}

TY - JOUR

T1 - 1,4-addition of alkyl halides to a side-on bound bafnocene dinitrogen complex

AU - Benito-Garagorri, David

AU - Bernskoetter, Wesley H.

AU - Lobkovsky, Emil

AU - Chirik, Paul J.

PY - 2009/8/24

Y1 - 2009/8/24

N2 - Attempts to functionalize the side-on coordinated dinitrogen ligand in [(eta; 5-C 5Me 4H) 2Hf] 2(μ 2, eta; 2 eta; 2-N 2) by addition of methyl halides such as CH 3X (X = Cl, Br, I) or alkyl halides (R-X = CH 3CH 2Br, CH 3CH 2I, and CH 3CH 2CH 2C1) resulted in 1,4-addition to yield metastable, weakly activated hafnocene end-on dinitrogen complexes, [(eta; 5-C 5Me 4H) 2HfR] (μ 2, (eta; 1, eta; 1-N 2) The product of methyl iodide addition, [(eta; 5-C 5Me 4H) 2HfCH 3](eta; 1, eta; 1-N 2) was structurally characterized and confirmed the hapticity of the N 2 ligand. Addition of the radical clocks 6-chloro-l-hexene and chloromethylcyclopropane also yielded 1,4-addition products with accompanying cyclization and ring-opening, respectively. In contrast, treatment of [(eta; 5-C 5Me 4H) 2Hf] 2-(μ 2, η 2, η 2-N 2) with benzyl chloride, benzyl bromide, or allyl bromide yielded only small quantities of the 1,4-addition product, with the majority of the mixture being the hafnocene dihalide (η 5-C 5Me 4H) 2HfX 2 and organic products of radical coupling. In benzene-d 6 solution at 23 °C, the 1,4-addition products undergo disproportionation with loss of N 2 to yield the hafnocene alkyl halide complexes (η 5-C 5Me 4H) 2Hf(R)X along with concomitant regeneration of the strongly activated side-on dinitrogen complex [(η 5-C 5Me 4H) 2(μ 2, η 2, η 2-N 2). This rearrangement is sensitive to both the halide and the alkyl substituents, where smaller groups undergo the most rapid rates of reaction, likely due to the accessibility of side-on bound N 2 intermediates.

AB - Attempts to functionalize the side-on coordinated dinitrogen ligand in [(eta; 5-C 5Me 4H) 2Hf] 2(μ 2, eta; 2 eta; 2-N 2) by addition of methyl halides such as CH 3X (X = Cl, Br, I) or alkyl halides (R-X = CH 3CH 2Br, CH 3CH 2I, and CH 3CH 2CH 2C1) resulted in 1,4-addition to yield metastable, weakly activated hafnocene end-on dinitrogen complexes, [(eta; 5-C 5Me 4H) 2HfR] (μ 2, (eta; 1, eta; 1-N 2) The product of methyl iodide addition, [(eta; 5-C 5Me 4H) 2HfCH 3](eta; 1, eta; 1-N 2) was structurally characterized and confirmed the hapticity of the N 2 ligand. Addition of the radical clocks 6-chloro-l-hexene and chloromethylcyclopropane also yielded 1,4-addition products with accompanying cyclization and ring-opening, respectively. In contrast, treatment of [(eta; 5-C 5Me 4H) 2Hf] 2-(μ 2, η 2, η 2-N 2) with benzyl chloride, benzyl bromide, or allyl bromide yielded only small quantities of the 1,4-addition product, with the majority of the mixture being the hafnocene dihalide (η 5-C 5Me 4H) 2HfX 2 and organic products of radical coupling. In benzene-d 6 solution at 23 °C, the 1,4-addition products undergo disproportionation with loss of N 2 to yield the hafnocene alkyl halide complexes (η 5-C 5Me 4H) 2Hf(R)X along with concomitant regeneration of the strongly activated side-on dinitrogen complex [(η 5-C 5Me 4H) 2(μ 2, η 2, η 2-N 2). This rearrangement is sensitive to both the halide and the alkyl substituents, where smaller groups undergo the most rapid rates of reaction, likely due to the accessibility of side-on bound N 2 intermediates.

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ER -

1,4-addition of alkyl halides to a side-on bound bafnocene dinitrogen complex

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