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Molecular titanium nitrides: nucleophiles unleashed.

Authors :: Grant LN
Pinter B
Kurogi T
Carroll ME
Wu G
Manor BC
Carroll PJ
Mindiola DJ
Source :: Chemical science [Chem Sci] 2017 Feb 01; Vol. 8 (2), pp. 1209-1224. Date of Electronic Publication: 2016 Sep 22.
Publication Year :: 2017
Abstract: In this contribution we present reactivity studies of a rare example of a titanium salt, in the form of [μ <subscript>2</subscript> -K(OEt <subscript>2</subscript> )] <subscript>2</subscript> [(PN) <subscript>2</subscript> Ti[triple bond, length as m-dash]N] <subscript>2</subscript> ( 1 ) (PN <superscript>-</superscript> = N -(2-(diisopropylphosphino)-4-methylphenyl)-2,4,6-trimethylanilide) to produce a series of imide moieties including rare examples such as methylimido, borylimido, phosphonylimido, and a parent imido. For the latter, using various weak acids allowed us to narrow the p K <subscript>a</subscript> range of the NH group in (PN) <subscript>2</subscript> Ti[triple bond, length as m-dash]NH to be between 26-36. Complex 1 could be produced by a reductively promoted elimination of N <subscript>2</subscript> from the azide precursor (PN) <subscript>2</subscript> TiN <subscript>3</subscript> , whereas reductive splitting of N <subscript>2</subscript> could not be achieved using the complex (PN) <subscript>2</subscript> Ti[double bond, length as m-dash]N[double bond, length as m-dash]N[double bond, length as m-dash]Ti(PN) <subscript>2</subscript> ( 2 ) and a strong reductant. Complete N-atom transfer reactions could also be observed when 1 was treated with ClC(O) <superscript>t</superscript> Bu and OCCPh <subscript>2</subscript> to form NC <superscript>t</superscript> Bu and KNCCPh <subscript>2</subscript> , respectively, along with the terminal oxo complex (PN) <subscript>2</subscript> Ti[triple bond, length as m-dash]O, which was also characterized. A combination of solid state <superscript>15</superscript> N NMR (MAS) and theoretical studies allowed us to understand the shielding effect of the counter cation in dimer 1 , the monomer [K(18-crown-6)][(PN) <subscript>2</subscript> Ti[triple bond, length as m-dash]N], and the discrete salt [K(2,2,2-Kryptofix)][(PN) <subscript>2</subscript> Ti[triple bond, length as m-dash]N] as well as the origin of the highly downfield <superscript>15</superscript> N NMR resonance when shifting from dimer to monomer to a terminal nitride (discrete salt). The upfield shift of <superscript>15</superscript> N <subscript>nitride</subscript> resonance in the <superscript>15</superscript> N NMR spectrum was found to be linked to the K <superscript>+</superscript> induced electronic structural change of the titanium-nitride functionality by using a combination of MO analysis and quantum chemical analysis of the corresponding shielding tensors.<br /> (This journal is © The Royal Society of Chemistry 2016.)