Alkali metal mediated bimetallic main group and transition organometallic chemistry

The work reported may appear as an eclectic mix of zinc, magnesium, aluminium and transition metal chemistry. However, at the heart of all the investigations is the prominent role of lithium or sodium within a bi-metallic species in either 1) facilitating unusual reactivity or 2) resulting in novel structural chemistry. The surprising transformation of saturated diamine (iPr)NHCH2CH2NH(iPr) to the unsaturated diazaethene [(iPr)NCH=CHN(iPr)]²⁻ via the synergic mixture BuM, (tBu)₂Zn and TMEDA (where M = Li, Na) has been investigated by NMR spectroscopy and DFT calculations. Isolated compounds (TMEDA)Li[(iPr)NCH₂CH₂NH(iPr)]Zn(tBu)₂ 18, (TMEDA)Li[(iPr)NCH₂CH₂CH₂N(iPr)]Zn(tBu) 21, {(THF)Li[(iPr)NCH₂CH₂N(iPr)]Zn(tBu)}₂ 22, and {(TMEDA)Na[(iPr)NCH₂CH₂N(iPr)]Zn(tBu)}₂ 31, are discussed in relation to their role in forming (TMEDA)M[(iPr)NCH=CHN(iPr)]Zn(tBu) (M = Li, 24; Na, 29). Also, the dilithiozincate molecular hydride [(TMEDA)Li]₂[(iPr)NCH₂CH₂N(iPr)]Zn(tBu)H 26 is reported. Its ⁷Li NMR spectrum reveals a rare scalar ¹JLi-H coupling constant of 13.3 Hz. The diisobutylamide ligand (DIBA) has been investigated in both a homo-metallic (Li) and bi-metallic (Li/Zn, Na/Zn) context. A zinc-rich zincate [(TMEDA)₂Li]⁺{(DIBA)[Zn(tBu)₂]₂}⁻ 38 and bis-amide (TMEDA)Na(DIBA)₂Zn(tBu)₂ 40 have been made. Reported also is the synthesis of the sodium complex [(Et₂O)Na]₄Cr₂Me₈ 44. Its drastically elongated Cr-Cr separation [3.24 Å], relative to the lithium species [1.98 Å], has revealed the important alkali metal role in dictating the nature of metal-metal interactions. The reactivity of 44 has been investigated towards Lewis bases, resulting in the novel heptamethyl chromium complex [(TMEDA)Na]₃Cr₂Me₇ 45. This new family of group VI sodium methyl compounds has also been extended to molybdenum via [(TMEDA)Na]₄Mo₂Me₈ 47. Finally, bimetallic aluminates (THF)Li(TMP)Al(iBu)₃ 49 and "Li(TMP)₂Al(iBu)₂" 48 have both previously demonstrated a propensity towards heteroatom activated sp³ deprotonation. To extend this potentially useful synthetic methodology the reactivity of both reagents has been systematically investigated towards a series of bi and tridentate substrates incorporating both nitrogen and oxygen atoms. A family of adducts of 49 have been prepared.The work reported may appear as an eclectic mix of zinc, magnesium, aluminium and transition metal chemistry. However, at the heart of all the investigations is the prominent role of lithium or sodium within a bi-metallic species in either 1) facilitating unusual reactivity or 2) resulting in novel structural chemistry. The surprising transformation of saturated diamine (iPr)NHCH2CH2NH(iPr) to the unsaturated diazaethene [(iPr)NCH=CHN(iPr)]²⁻ via the synergic mixture BuM, (tBu)₂Zn and TMEDA (where M = Li, Na) has been investigated by NMR spectroscopy and DFT calculations. Isolated compounds (TMEDA)Li[(iPr)NCH₂CH₂NH(iPr)]Zn(tBu)₂ 18, (TMEDA)Li[(iPr)NCH₂CH₂CH₂N(iPr)]Zn(tBu) 21, {(THF)Li[(iPr)NCH₂CH₂N(iPr)]Zn(tBu)}₂ 22, and {(TMEDA)Na[(iPr)NCH₂CH₂N(iPr)]Zn(tBu)}₂ 31, are discussed in relation to their role in forming (TMEDA)M[(iPr)NCH=CHN(iPr)]Zn(tBu) (M = Li, 24; Na, 29). Also, the dilithiozincate molecular hydride [(TMEDA)Li]₂[(iPr)NCH₂CH₂N(iPr)]Zn(tBu)H 26 is reported. Its ⁷Li NMR spectrum reveals a rare scalar ¹JLi-H coupling constant of 13.3 Hz. The diisobutylamide ligand (DIBA) has been investigated in both a homo-metallic (Li) and bi-metallic (Li/Zn, Na/Zn) context. A zinc-rich zincate [(TMEDA)₂Li]⁺{(DIBA)[Zn(tBu)₂]₂}⁻ 38 and bis-amide (TMEDA)Na(DIBA)₂Zn(tBu)₂ 40 have been made. Reported also is the synthesis of the sodium complex [(Et₂O)Na]₄Cr₂Me₈ 44. Its drastically elongated Cr-Cr separation [3.24 Å], relative to the lithium species [1.98 Å], has revealed the important alkali metal role in dictating the nature of metal-metal interactions. The reactivity of 44 has been investigated towards Lewis bases, resulting in the novel heptamethyl chromium complex [(TMEDA)Na]₃Cr₂Me₇ 45. This new family of group VI sodium methyl compounds has also been extended to molybdenum via [(TMEDA)Na]₄Mo₂Me₈ 47. Finally, bimetallic aluminates (THF)Li(TMP)Al(iBu)₃ 49 and "Li(TMP)₂Al(iBu)₂" 48 have both previously demonstrated a propensity towards heteroatom activated sp³ deprotonation. To extend this potentially useful synthetic methodology the reactivity of both reagents has been systematically investigated towards a series of bi and tridentate substrates incorporating both nitrogen and oxygen atoms. A family of adducts of 49 have been prepared