N,N′‐Bis(2,6‐diisopropylphenyl)benzamidinates and ‐pivalamidinates of the s‐Block Metals Lithium, Potassium, and Calcium

Abstract

Metalation of N, benzamidine (1a) and -pivalamidine (1b) in tetrahydrofuran (THF) with nbutyllithium and potassium bis(trimethylsilyl)amide gives the corresponding N,NЈ-bis(2,6-diisopropylphenyl)benzamidinates and -pivalamidinates of lithium, [(thf) ). Because metalation of these amidines is not possible with [(thf) 2 Ca{N(SiMe 3 ) 2 } 2 ], a metathetical approach has been [a] 1312 chosen. Hence, the reaction of 3a with calcium iodide in THF yields (tetrahydrofuran)calcium bis[N,NЈ-bis(2,6-diisopropylphenyl)benzamidinate] (4a). For the bulkier N,NЈ-bis(2,6diisopropylphenyl)pivalamidinate, heteroleptic [(thf)Ca-{(Dipp-N) 2 C-tBu}{N(SiMe 3 ) 2 }] (4b) forms. Depending on the softness and charge-to-radius ratio, syn configuration of the amidinate ligands is observed for 2a, 4a, and 4b, whereas the anti configuration is realized in complexes 2b, 3a, and 3b, the latter being stabilized by intramolecular metal-π interactions.

Potassium Salts of Asymmetrically Substituted Amidinates and a Triazenide

“…Anti-configuration is realized if steric intra-ligand strain induced by two very bulky N-bound aryl groups enforce an orientation of one aryl group to the opposite side than the C-bound group (entries 8-11, 15, 19, 22, and 23). One bulky aryl substituent seems to be sufficient to favor anti-configuration of the amidinate ligands (entries [16][17][18]. One bulky aryl substituent seems to be sufficient to favor anti-configuration of the amidinate ligands (entries [16][17][18].…”

“…[11] 19 C-tBu Dipp Dipp Anti [18] 20 C-tBu Dipp CH 2 -Fu Syn-Z [20] 21 C-tBu Dipp CH 2 -Py Syn-Z [20] 22 C-Ad Dipp C 6 H 2 -(CHPh 2 ) 2 iPr Anti [21] 23 C-NiPr 2 Dipp Dipp Anti [22] 24 C-N=CtBu 2 C 6 H 2 -(CHPh 2 ) 2 tBu C 6 H 2 -(CHPh 2 ) 2 tBu Syn-E [23] 25 C-CH 2 -NHC Dipp Dipp Anti [24] 26 N pTol pTol Syn-E [6] 27 N C 6 H 4 -4-NO 2 C 6 H 4 -4-NO 2 Syn-E [8] 28 N Mes Mes Syn-E [10] 29 N C 6 H 4 -Mes C 6 H 3 -Mes 2 Syn-E [9] 30 N C 6 H 4 -Trip C 6 H 4 -Trip Syn-E [7] 31 N C 6 H 4 -Trip C 6 H 3 -Mes 2 Syn-E [9] 32 N C 6 H 3 (C 6 H 3 Me 2 ) 2 C 6 H 3 (C 6 H 3 Me 2 ) 2 Syn-E [9] The influence of the middle moiety E can be evaluated considering similar amidinate (entries 12 and 13) and triazenide molecules (entry 32) which crystallize with (syn-E)-isomeric ligands.…”

Surprisingly Different Reaction Behavior of Alkali and Alkaline Earth Metal Bis(trimethylsilyl)amides toward Bulky N‐(2‐Pyridylethyl)‐N′‐(2,6‐diisopropylphenyl)pivalamidine

“…The bulky tridentate Lewis base N ‐(2‐pyridylethyl)‐ N′ ‐(2,6‐diisopropylphenyl)pivalamidine ( 1 ) was prepared by the reaction of N ‐(2,6‐diisopropylphenyl)pivalimidoyl chloride with an equimolar amount of 2‐(aminoethyl)pyridine in boiling toluene (reaction 1). Recrystallization from toluene yielded the syn ‐ Z ‐isomer of 1 in the crystalline state.…”

“…The N,N′ ‐bis(2,6‐diisopropylphenyl)benz‐ and ‐pivalamidinates (R=Ph and t Bu, respectively) of potassium (Scheme , A ) and calcium (Scheme , B 1 and B 2 ) bind through the nitrogen atoms and the negative charge is widely delocalized throughout the syn ‐ E ‐isomeric 1,3‐diazaallyl moiety in each case (the prefix syn or anti refer to the N‐bound organic groups neglecting the metal atoms). The ytterbium (not shown) and samarium complexes ( C ) bind to the anti ‐ Z ‐isomeric N,N′ ‐bis(2,6‐diisopropylphenyl)pivalamidinate resulting in strong metal π‐interactions to one 2,6‐diisopropylphenyl group (Dipp) .…”

Hexanuclear Wheel‐Shaped Lithium N‐(2,6‐Diisopropylphenyl)‐N′‐(2‐pyridylethyl)benzamidinate

“…However, strong multidentate coligands like N , N , N ′, N ′′, N ′′‐pentamethyldiethylenetriamine hinder a symmetric binding to the lithium ions and then ( syn‐E )‐isomeric amidinates act as monodentate ligands . The less favorable ( syn‐Z )‐ and ( anti‐Z )‐isomeric amidinate ions are stabilized by steric repulsion between sterically demanding groups R and bulky N ‐bound substituents enforcing ( anti‐Z )‐,, , ( anti ‐ E )‐, and ( syn‐Z )‐coordination modes . Groups R and R ′ containing Lewis basic donor sites are able to stabilize ( anti‐E )‐ and ( syn‐Z )‐isomeric amidinates.…”