Abstract. Reaction of Sr(2-Me 2 N-α-Me 3 Si-benzyl) 2 ·(THF) 2 with one equivalent of DIPP(H)N-BH-N(H)DIPP (NBN-H 2 , DIPP = 2,6-iPr-phenyl) gave the strontium bora-amidinate complex Sr(NBN)·(THF) 4 . Traces of silicone grease, however, can change the course of the reaction completely and gave the product {Sr[(DIPP)NSiMe 2 O]·THF} 4 (1) in a ca. 25 % yield. Complex 1 is a S 4 symmetric cluster with a Sr 4 O 4 core and four chelating amide side arms. From the mother liquor a second product could be isolated: the

The dibenzo[b,f ]azepinate (DBAP) complexes (DBAP)Li•(THF) 3 , (DBAP) 2 Mg•(THF) 2 , and (DBAP) 2 Ca•(THF) 3 could be isolated as highly air-sensitive compounds in yields of 93%, 72%, and 48%, respectively. Crystal structures of these THF adducts reveal monomeric complexes in which the degree of ring puckering depends on the nature of the metal. The most extreme deviation from planarity is found for the most covalent bound metal, Mg, but in all cases no interaction between the metal and the azepine CC bond is observed. The THF-free complex [(DBAP) 2 Mg] 2 , which could be obtained in 77% yield, crystallizes as an unusual dimer with three bridging and one terminal DBAP ligand. The bridging DBAP ligands are highly bent and span a cavity in which a Mg 2+ ion is bound through three alkene−Mg interactions with an average Mg•••C distance of 2.794(3) Å. Theoretical calculations support these contacts. A combination of AIM and NPA analyses shows polarization of the alkene π-electron density toward the metal (vertical polarization) but also demonstrates a polarization of electron density toward the C atom closest to Mg (horizontal polarization). Such metal−alkene interactions and implicit CC bond polarization are key features in main group metal catalyzed alkene conversions.

One-pot reaction of 2,6-iPr 2 -aniline (DIPP-NH 2 ) with (Me 2 SiO) 3 and Sr[N(SiMe 3 ) 2 ] 2 (SrN′′ 2 ) gave a tetranuclear cluster consisting of four dianions [OSiMe 2 N-DIPP] 2and four Sr 2+ ions solvated each by one THF ligand. The general applicability of this method was investigated by variation of amine and metal. Anilines with smaller substituents led to insoluble uncharacterized coordination polymers, whereas bulkier anilines gave soluble product mixtures that could not be purified. Primary alkylamines neither led to isolable products. Introduction of a tBu group in para-position of DIPP-NH 2 , however, gave an isostruc- [a]

Strontium complexes are presented with two different bulky amidinate ligands (Am): tBuC(N-DIPP) 2 (DIPP = 2,6-diisopropylphenyl), abbreviated here as tBuAm DIPP , and (p-tolyl)C(N-Ar ‡ ) 2 (Ar ‡ = 2,6-Ph 2 CH-4-iPrphenyl) abbreviated here as pTolAm Ar ‡ . The amidine tBuAm DIPP -H was deprotonated by Sr[N(SiMe 3 ) 2 ] 2 in benzene at 60 °C. Although the product, tBuAm DIPP SrN-(SiMe 3 ) 2 , could be characterized by NMR, attempts to isolate it led to ligand scrambling via a Schlenk equilibrium. Reaction of in situ prepared tBuAm DIPP SrN(SiMe 3 ) 2 with PhSiH 3 gave PhH 2 SiN(SiMe 3 ) 2 and presumably the intermediate tBuAm DIPP SrH, but the latter is not stable and the homoleptic complex (tBuAm DIPP ) 2 Sr was isolated and structurally characterized. Deprotonation of the bulkier amidine pTolAm Ar ‡ -H with Sr[N(SiMe 3 ) 2 ] 2 needed forcing conditions, inevitably giving rise to deprotonation of the Ph 2 CH substituent as well. Reaction of pTolAm Ar ‡ -H with the less bulky and less basic Sr[N(SiHMe 2 ) 2 ] 2 , however, gave the heteroleptic product pTolAm Ar ‡ SrN(SiHMe 2 ) 2 , which has been structurally characterized. The latter was also at 60 °C stable toward ligand scrambling. Reaction with PhSiH 3 did give hydride exchange, but the product pTolAm Ar ‡ SrH decomposed even at −30 °C. Instead, an amidinate complex with a deprotonated Ph 2 CH substituent was isolated and structurally characterized (7). The latter catalyzed the intramolecular alkene hydroamination.

Syntheses and crystal structures of the monomeric bora-amidinate (bam) complexes NBN-Mg·(THF) and NBN-Ca·(THF) are presented; NBN = HB[N(2,6-iPr-CH)]. The simplicity of their H NMR spectra in THF-d suggest that their monomeric solid state structures are retained in solution. NBN-Mg·(THF) in CD, however, is in equilibrium with a dimeric species. Calculations (B3PW91/6-311++G**) reveal a very high localized negative charge (NPA: -1.103) on the N atoms in NBN-Mg. The strongly basic properties of the bam ligand are in agreement with catalytic activity of these complexes in the intramolecular alkene hydroamination. A mechanism is proposed in which the bam ligand is non-innocent and cooperative, playing an active role in substrate deprotonation and product protonation.