Synthesis and M-Cγ hemilability of group 2 bis(phosphinimino)methanides

Shabana A. Ahmed; Michael S. Hill; Peter B. Hitchcock

doi:10.1021/om050811h

Synthesis and M-C_γ hemilability of group 2 bis(phosphinimino)methanides

Shabana A. Ahmed, Michael S. Hill, Peter B. Hitchcock

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Abstract

The sterically demanding bis(phosphinimino)methanide [CH(Ph ₂PNC₆H₂-2,4,6-Me₃)₂] ^-, formed by deprotonation of the bis(phosphinimino)methane [CH ₂(Ph₂PNC₆H₂-2,4,6-Me ₃)₂], has been employed in the synthesis of a variety of homo- and heteroleptic complexes of the group 2 metals Mg, Ca, Sr, and Ba. The crystallographically characterized magnesium complexes, the dimer [{CH(Ph ₂PNC₆H₂-2,4,6-Me₃) ₂}MgCl]₂ and the monomer [{CH(Ph₂PNC ₆H₂-2,4,6-Me₃)₂}MgCl(THF)], were synthesized in a similar manner by deprotonation of the ligand precursor with MeMgCl but crystallized either without or in the presence of THF. The synthetically useful [{CH(Ph₂PNC₆H₂-2,4,6- Me₃)₂}K], formed from [CH₂(Ph ₂-PNC₆H₂-2,4,6-Me₃)₂] and [KN(SiMe₃)₂] in toluene, was shown in the solid state to consist of dimeric species formed by K-mesityl multihapto interactions. Homoleptic [{CH(Ph₂PNC₆H₂-2,4,6-Me ₃)₂}₂Ae] (Ae = Ca and Ba) and heteroleptic [{CH(Ph₂PNC₆H₂-2,4,6-Me₃) ₂}AeN(SiMe₃)₂(THF)] (Ae = Ca, Sr) complexes of the heavier alkaline earth metals Ca, Sr, and Ba were most readily provided by a "one-pot" procedure utilizing the appropriate AeI₂ reagent and variation of [CH₂(Ph₂PNC₆H ₂-2,4,6-Me₃)₂] and [KN-(SiMe₃) ₂] stoichiometry in THF. The complexes were shown by ³¹P{¹H} NMR to adopt variable and hemilabile (ΔG^‡ = ca. 50 kJ mol^-1) coordination geometries involving, most likely, M-C_γ coordination and re-coordination. The ionic nature of the bonding was also implicated in our lack of success in the application of these complexes in reactivity studies with a variety of bulky protic reagents. This behavior was investigated by DFT (B3LYP/LANL2DZ) methods to highlight the differences in NBO charge distribution between model ionic bis(phosphinimino)methanide and β-diketiminato complexes.

Original language	English
Pages (from-to)	394-402
Number of pages	9
Journal	Organometallics
Volume	25
Issue number	2
DOIs	https://doi.org/10.1021/om050811h
Publication status	Published - 16 Jan 2006

ASJC Scopus subject areas

Physical and Theoretical Chemistry
Organic Chemistry
Inorganic Chemistry

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@article{46f990be123b4819b99353ad49e46424,

title = "Synthesis and M-Cγ hemilability of group 2 bis(phosphinimino)methanides",

abstract = "The sterically demanding bis(phosphinimino)methanide [CH(Ph 2PNC6H2-2,4,6-Me3)2] -, formed by deprotonation of the bis(phosphinimino)methane [CH 2(Ph2PNC6H2-2,4,6-Me 3)2], has been employed in the synthesis of a variety of homo- and heteroleptic complexes of the group 2 metals Mg, Ca, Sr, and Ba. The crystallographically characterized magnesium complexes, the dimer [{CH(Ph 2PNC6H2-2,4,6-Me3) 2}MgCl]2 and the monomer [{CH(Ph2PNC 6H2-2,4,6-Me3)2}MgCl(THF)], were synthesized in a similar manner by deprotonation of the ligand precursor with MeMgCl but crystallized either without or in the presence of THF. The synthetically useful [{CH(Ph2PNC6H2-2,4,6- Me3)2}K], formed from [CH2(Ph 2-PNC6H2-2,4,6-Me3)2] and [KN(SiMe3)2] in toluene, was shown in the solid state to consist of dimeric species formed by K-mesityl multihapto interactions. Homoleptic [{CH(Ph2PNC6H2-2,4,6-Me 3)2}2Ae] (Ae = Ca and Ba) and heteroleptic [{CH(Ph2PNC6H2-2,4,6-Me3) 2}AeN(SiMe3)2(THF)] (Ae = Ca, Sr) complexes of the heavier alkaline earth metals Ca, Sr, and Ba were most readily provided by a {"}one-pot{"} procedure utilizing the appropriate AeI2 reagent and variation of [CH2(Ph2PNC6H 2-2,4,6-Me3)2] and [KN-(SiMe3) 2] stoichiometry in THF. The complexes were shown by 31P{1H} NMR to adopt variable and hemilabile (ΔG‡ = ca. 50 kJ mol-1) coordination geometries involving, most likely, M-Cγ coordination and re-coordination. The ionic nature of the bonding was also implicated in our lack of success in the application of these complexes in reactivity studies with a variety of bulky protic reagents. This behavior was investigated by DFT (B3LYP/LANL2DZ) methods to highlight the differences in NBO charge distribution between model ionic bis(phosphinimino)methanide and β-diketiminato complexes.",

author = "Ahmed, {Shabana A.} and Hill, {Michael S.} and Hitchcock, {Peter B.}",

year = "2006",

month = jan,

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doi = "10.1021/om050811h",

language = "English",

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pages = "394--402",

journal = "Organometallics",

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TY - JOUR

T1 - Synthesis and M-Cγ hemilability of group 2 bis(phosphinimino)methanides

AU - Ahmed, Shabana A.

AU - Hill, Michael S.

AU - Hitchcock, Peter B.

PY - 2006/1/16

Y1 - 2006/1/16

N2 - The sterically demanding bis(phosphinimino)methanide [CH(Ph 2PNC6H2-2,4,6-Me3)2] -, formed by deprotonation of the bis(phosphinimino)methane [CH 2(Ph2PNC6H2-2,4,6-Me 3)2], has been employed in the synthesis of a variety of homo- and heteroleptic complexes of the group 2 metals Mg, Ca, Sr, and Ba. The crystallographically characterized magnesium complexes, the dimer [{CH(Ph 2PNC6H2-2,4,6-Me3) 2}MgCl]2 and the monomer [{CH(Ph2PNC 6H2-2,4,6-Me3)2}MgCl(THF)], were synthesized in a similar manner by deprotonation of the ligand precursor with MeMgCl but crystallized either without or in the presence of THF. The synthetically useful [{CH(Ph2PNC6H2-2,4,6- Me3)2}K], formed from [CH2(Ph 2-PNC6H2-2,4,6-Me3)2] and [KN(SiMe3)2] in toluene, was shown in the solid state to consist of dimeric species formed by K-mesityl multihapto interactions. Homoleptic [{CH(Ph2PNC6H2-2,4,6-Me 3)2}2Ae] (Ae = Ca and Ba) and heteroleptic [{CH(Ph2PNC6H2-2,4,6-Me3) 2}AeN(SiMe3)2(THF)] (Ae = Ca, Sr) complexes of the heavier alkaline earth metals Ca, Sr, and Ba were most readily provided by a "one-pot" procedure utilizing the appropriate AeI2 reagent and variation of [CH2(Ph2PNC6H 2-2,4,6-Me3)2] and [KN-(SiMe3) 2] stoichiometry in THF. The complexes were shown by 31P{1H} NMR to adopt variable and hemilabile (ΔG‡ = ca. 50 kJ mol-1) coordination geometries involving, most likely, M-Cγ coordination and re-coordination. The ionic nature of the bonding was also implicated in our lack of success in the application of these complexes in reactivity studies with a variety of bulky protic reagents. This behavior was investigated by DFT (B3LYP/LANL2DZ) methods to highlight the differences in NBO charge distribution between model ionic bis(phosphinimino)methanide and β-diketiminato complexes.

AB - The sterically demanding bis(phosphinimino)methanide [CH(Ph 2PNC6H2-2,4,6-Me3)2] -, formed by deprotonation of the bis(phosphinimino)methane [CH 2(Ph2PNC6H2-2,4,6-Me 3)2], has been employed in the synthesis of a variety of homo- and heteroleptic complexes of the group 2 metals Mg, Ca, Sr, and Ba. The crystallographically characterized magnesium complexes, the dimer [{CH(Ph 2PNC6H2-2,4,6-Me3) 2}MgCl]2 and the monomer [{CH(Ph2PNC 6H2-2,4,6-Me3)2}MgCl(THF)], were synthesized in a similar manner by deprotonation of the ligand precursor with MeMgCl but crystallized either without or in the presence of THF. The synthetically useful [{CH(Ph2PNC6H2-2,4,6- Me3)2}K], formed from [CH2(Ph 2-PNC6H2-2,4,6-Me3)2] and [KN(SiMe3)2] in toluene, was shown in the solid state to consist of dimeric species formed by K-mesityl multihapto interactions. Homoleptic [{CH(Ph2PNC6H2-2,4,6-Me 3)2}2Ae] (Ae = Ca and Ba) and heteroleptic [{CH(Ph2PNC6H2-2,4,6-Me3) 2}AeN(SiMe3)2(THF)] (Ae = Ca, Sr) complexes of the heavier alkaline earth metals Ca, Sr, and Ba were most readily provided by a "one-pot" procedure utilizing the appropriate AeI2 reagent and variation of [CH2(Ph2PNC6H 2-2,4,6-Me3)2] and [KN-(SiMe3) 2] stoichiometry in THF. The complexes were shown by 31P{1H} NMR to adopt variable and hemilabile (ΔG‡ = ca. 50 kJ mol-1) coordination geometries involving, most likely, M-Cγ coordination and re-coordination. The ionic nature of the bonding was also implicated in our lack of success in the application of these complexes in reactivity studies with a variety of bulky protic reagents. This behavior was investigated by DFT (B3LYP/LANL2DZ) methods to highlight the differences in NBO charge distribution between model ionic bis(phosphinimino)methanide and β-diketiminato complexes.

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JO - Organometallics

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Synthesis and M-C_γ hemilability of group 2 bis(phosphinimino)methanides

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