Co(II) Amide, Pyrrolate, and Aminopyridinate Complexes: Assessment of their Manifold Structural Chemistry and Thermal Properties**

Abstract

A series of cobalt(II) (silyl)amides, pyrrolates and aminopyridinates were synthesized. Inspired by the dimeric bis (trimethylsilylamido)cobalt(II) complex ([Co(TMSA) 2 ] 2 ), facile salt metathesis employing the ligand 2,2,5,5-tetramethyl-1,2,5-azadisilolidinyl (TMADS) yielded its congener [Co(TMADS) 2 ] 2 . Novel, heteroleptic Lewis adducts of the former resulted in unusual three-to four-fold coordination geometry around the metal center. Similarily, the salt [Li(DAD) 2 ][Co(TMADS) 3 ] was isolated which demonstrates an ion separated Co(II) anion with silylamide ligation and Li + counter cation. Transpyrrolylation using [Co(TMSA) 2 ] 2 was established for the synthesis of bis[N,N'-2-(dimethylaminomethyl)pyrrolyl]cobalt(II), and bis(N-2-(tertbutyliminomethyl)pyrrolyl)cobalt(II). Treatment of CoCl 2 with two equivalents of lithiated N,N-dimethyl(N'-tert-butyl)ethane-1amino-2-amide and N,N-dimethyl(N'-trimethylsilyl)ethane-1amino-2-amide resulted in the respective Co(II) amido-amines. Reaction of CoCl 2 with lithium 4-methyl-N-(trimethylsilyl) pyridine-2-amide yielded the first binuclear, homoleptic Co(II) aminopyridinate complex with a distorted trigonal bipyramidal coordination environment (τ 5 = 0.533) for one central Co(II) ion and a weakly distorted tetrahedral coordination geometry (τ 4 = 0.845) for the other. All of the new compounds were thoroughly characterized in terms of composition and structure. Finally, the key thermal characteristics of volatility and thermal stability were assessed using a combination of thermogravimetric analysis and complementary bulk sublimation experiments.

An Unusual Tri‐coordinate Co(II) Silylamide with Potential for Chemical Vapor Deposition Processes

“…On the other hand, Evans NMR in benzene/deuterated benzene gave an estimate of the effective magnetic moment μ eff of 4.2(1) μ B , which was close to the spin‐only value of 3.9 μ B expected for Co(II) high spin ions. This was in the range of solution magnetic moments reported for tri‐coordinate Co(II) complexes, albeit at the lower end [3–5,10,14] . Magnetic moments around and above 5 μ B were prior observed for compounds consisting of two cation bearing moieties bridged by a ligand such as [Co(TMSA) 2 ] 2 (μ‐TMEDA)] (μ eff =5.1 μ B ) [4] or for complexes being in a dimer‐monomer solution equilibrium such as [Co(TMSA) 2 ] 2 (μ eff =4.7–5.7 μ B ) [3] .…”

“…Consequently, we employed TGA data to establish a Clausius‐Clapeyron model that allowed to estimate the 1 Torr temperature of the precursor to be 144 °C (Figure 2 c)) [22] . This value and the appurtenant Langmuir equation that described the overall vapor pressure – temperature correlation compared favorably with thermal data for structurally related Co silylamides: The parent complex [Co(TMSA) 2 ] 2 was found to exhibit a 1 Torr temperature of 106 °C in a prior study that also presented N,N‐dimethyl‐(N‐trimethylsilyl)ethane‐1‐amino‐2‐amido ligated Co(TMSAEDMA) 2 with a 1 Torr temperature of 152 °C [10] . Notably, the latter aminoamido ligand resembled the aminoamido ligand employed in this study to some extent.…”

“…[22] This value and the appurtenant Langmuir equation that described the overall vapor pressure -temperature correlation compared favorably with thermal data for structurally related Co silylamides: The parent complex [Co(TMSA) 2 ] 2 was found to exhibit a 1 Torr temperature of 106 °C in a prior study that also presented N,Ndimethyl-(N-trimethylsilyl)ethane-1-amino-2-amido ligated Co(TMSAEDMA) 2 with a 1 Torr temperature of 152 °C. [10] Notably, the latter aminoamido ligand resembled the aminoamido ligand employed in this study to some extent. Similarly, Co(II) geminal aminoamides such as Co(gDAS) 2 , [23] or Co(IV) geminal diamides such as Co(DTBgDAS) 2 [24] had 1 Torr temperatures of 112 °C and 150 °C, respectively.…”

“…This was in the range of solution magnetic moments reported for tri-coordinate Co(II) complexes, albeit at the lower end. [3][4][5]10,14] Magnetic moments around and above 5 μ B were prior observed for compounds consisting of two cation bearing moieties bridged by a ligand such as [Co(TMSA) 2 ] 2 (μ-TMEDA)] (μ eff = 5.1 μ B ) [4] or for complexes being in a dimer-monomer solution equilibrium such as [Co(TMSA) 2 ] 2 (μ eff = 4.7-5.7 μ B ). [3] Based on this, we expected a monomeric structure with trigonal coordination environment around the Co(II) center for 1, in which the chelating ligand did not only feature a cobalt amide, but also a weaker amino cobalt bond.…”

“…[9] Motivated by the employment of the well-known bis(bis(trimethylsilyl)amido) cobalt(II) [Co(TMSA) 2 ] THF adduct in thermal ALD for the deposition of CoO and Co(OH) 2 thin films, we recently evaluated a series of [Co(TMSA) 2 ] based adducts alongside amidoamine ligated Co(II) complexes in terms of their CVD/ALD applicability. [10] Transamination reactions employing dimeric [Co(TMSA) 2 ] 2 and the respective protio-ligand were identified as a facile route towards homoleptic, tetrahedral Co(II) complexes possessing high thermal stability and appreciable volatility, both of which are key requirements for precursor candidates. [11] Interested to explore the feasibility of the transamination approach for the synthesis of trigonal planar Co(II) complexes through selective replacement of just one TMSA ligand, we identified a series of ethane-backbone-bridged diamines, namely N,N'-di-tert-butyl-ethanediamine, N,N',N'trimethylethanediamine, N,N-dimethyl(N'-tert-butyl)ethane-1,2diamine and lastly rac-N 2 ,N 3 -di-tert-butylbutane-2,3-diamine as suitable aspirants.…”