The concept and the first example for electronic frustration within a C-B π-bond arising from the competition for a lone pair of electrons is reported. The α-borylated phosphorus ylide (α-BCP) Ph PC(CH )BEt (1) has been synthesized, characterized, and investigated with the aid of density functional theory calculations. These show the presence of a highly polarized C-B π-bond, induced by the electron-withdrawing Ph P substituent. This competition for the C-based lone pair of electrons leads to an FLP-type reactivity (FLP=frustrated Lewis pair), which has been demonstrated by reacting 1 with various small molecules: the dimeric insertion products [Ph PC(CH )COBEt ] (2) and [Ph PC(CH )(CO )BEt ] (5) result from the reaction of 1 with CO and CO , respectively, whereas monomeric products of the general formula [Ph PC(CH )(XYZ)BEt ] were obtained by treating 1 with COS (3), CS (4) or the heterocumulenes PhNCO (6) and PhNCS (7).

The synthesis and characterization of two bulky ferrocenyl-functionalized amidinates and their lithium, potassium, rhodium­(I), and iridium­(I) complexes are reported. The ferrocenyl mono­(amidine) [Fc­{C­(NDipp)­(NHDipp)}] (1) (Fc = ferrocenyl; Dipp = 2,6-diisopropylphenyl) and its potassium complex [Fc­{C­(NDipp)2K}·3THF] (2) as well as the 1,1′-ferrocendiyl-bridged bis­(amidinate) [fc­{C­(NMes)2Li}2·3THF] (3) (fc = ferrocene-1,1′-diyl; Mes = mesityl) were synthesized. Salt metathesis reactions with the metal precursors [Rh­(cod)­Cl]2 (cod = 1,5-cyclooctadiene) and [Ir­(cod)­Cl]2 gave the rhodium­(I) and iridium­(I) complexes [Fc­{C­(NDipp)2Rh­(cod)}] (4), [fc­{C­(NMes)2Rh­(cod)}2] (5), and [fc­{C­(NMes)2Ir­(cod)}2] (6), as well as the ortho-metalated compound [(Cp)­Fe­(C5H3)­{C­(NHDipp)­(NDipp)­Ir­(cod)}] (7). As complex 7 showed an ortho-metalation on the ferrocene backbone, we investigated this reaction in more detail. It was found that the rhodium­(I) complexes 4 and 5 also undergo ortho-metalation upon treatment with carbon monoxide (CO). After the carbonylation, the first known ortho-metalation of rhodium­(I) on ferrocene complexes was observed for [(Cp)­Fe­{(C5H3)­C­(NHDipp)­(NDipp)­Rh­(CO)2}] (8) and [Fe­(C5H3)2{C­(NHMes)­(NMes)­Rh­(CO)2}2] (9). A combined electrochemical and quantum chemical study revealed that depending on both the metal-bound ligand (CO vs cod) and the bonding mode (κ2 N vs ortho-metalated), the highest occupied molecular orbital is located more on iron or on rhodium/iridium.

The synthesis and characterization of several rhodium(I) complexes of amidinate and linker-bridged bis(amidinate) ligands are presented. The amidinate ligands for the mononuclear complexes CH 3 {C(NMes) 2 Rh(cod)} (1), CH 3 -{C(NDipp) 2 Rh(cod)} (2), and HCC{C(NDipp) 2 Rh(cod)} (3) (cod = 1,5-cyclooctadiene) were synthesized by reacting the corresponding organometallic precursor [Rh(cod)Cl] 2 with the alkali metal amidinates CH 3 {C(NR) 2 Li} L1Li (R = Mes = 2,4,6-Me 3 C 6 H 2 ) and L2Li (R = Dipp = 2,6-iPr 2 C 6 H 3 ). Analogously, the alkynylfunctionalized sodium amidinate (HCC{C(NDipp) 2 Na}·2DME, L3Na) could be further deprotonated and reacted with carbodiimine to form the alkyne-bridged bis(amidinate) CC{C(NDipp) 2 -Na(thf )} 2 (L4Na), which serves as suitable starting material for the synthesis of CC{C(NDipp) 2 Rh(cod)} 2 (4). The bis(amidinate) ligands for the corresponding para-(5) and meta-(6) phenyl- [a] 3024 Scheme 4. Synthesis of L5Na and L6Na via their protonated analogues L5H and L6 H, respectively PPSE (polyphosphoric acid trimethylsilyl ester).

The synthesis and characterisation of two aluminium diphosphamethanide complexes, [Al(tBu)2 {κ(2) P,P'-Mes*PCHPMes*}] (3) and [Al(C6 F5 )2 {κ(2) P,P'-Mes*PCHPMes*}] (4), and the silylated analogue, Mes*PCHP(SiMe3 )Mes* (5), are reported. The aluminium complexes feature four-membered PCPAl core structures consisting of diphosphaallyl ligands. The silylated phosphine 5 was found to be a valuable precursor for the synthesis of 4 as it cleanly reacts with the diaryl aluminium chloride [(C6 F5 )2 AlCl]2 . The aluminium complex 3 reacts with molecular dihydrogen at room temperature under formation of the acyclic σ(2) λ(3) ,σ(3) λ(3) -diphosphine Mes*PCHP(H)Mes* and the corresponding dialkyl aluminium hydride [tBu2 AlH]3 . Thus, 3 belongs to the family of so-called hidden frustrated Lewis pairs.

We present the synthesis of a series of NHC‐stabilized iron(II) complexes of the type [Fe(NHC)2Mes2] and [Fe(NHC)Mes2], starting from [Fe2Mes4] and the NHC. Depending on the steric demand of the NHC used, tetrahedral {[Fe(Me2Im)2Mes2] 1 and [Fe(MeiPrIm)2Mes2] 2}, square‐planar {trans‐[Fe(iPr2Im)2Mes2] 3}, or trigonal‐planar {[Fe(R2Im)Mes2]; R = tBu 6, Dipp 7, Dipp2H2 8} complexes were isolated. Three‐coordinate complexes [Fe(R2Im)Mes2] (R = Me 4, iPr 5) of smaller carbenes were synthesized via ligand exchange of [Fe(NHC)2Mes2] and [Fe2Mes4]. The reactivity of trans‐[Fe(iPr2Im)2Mes2] 3 towards small molecules and element–hydrogen compounds was investigated. The reaction of 3 and 2 with dioxygen led to the tetrameric‐cluster complexes [{Fe(R2Im)(OMes)(µ2‐O)}4] 9 and 10 (R = iPr 9, Me 10). The reaction of 3 with CO afforded [Fe(iPr2Im)2(CO)3] 11. Reactions of 3 with E–H compounds (E = O, S, N, P, Sn), with substitution of the mesityl ligands, produced the complexes [Fe(iPr2Im)2(OtBu)2] 12, [Fe(iPr2Im)2(OPh)2] 13, [Fe(iPr2Im)2(SPh)2] 14, [Fe(iPr2Im)2(NHPh)2] 15, cis‐[Fe(iPr2Im)2{o‐C6H4(NH)2}] 16, [Fe(iPr2Im)2(PHPh)2] 17, [Fe(iPr2Im)2(PPh2)2] 18, trans‐[Fe(Me2Im)2(SnnBu3)2] 19, and trans‐[Fe(iPr2Im)2(SnnBu3)2] 20. The complexes 16, 17, 19, and 20 adopt square‐planar structures. The reaction of 3 with phenylsilane afforded crystallographically characterized [Fe(iPr2Im)2(µ2‐H)3(SiPh2H){SiH2(iPr2Im)}] 21.