Stabilization of Pentaphospholes as η⁵‐Coordinating Ligands

Abstract

Electrophilic functionalisation of [Cp*Fe(h 5-P 5)] (1) yields the first transition-metal complexes of pentaphospholes (cyclo-P 5 R). Silylation of 1 with [(Et 3 Si) 2 (m-H)][B-(C 6 F 5) 4 ] leads to the ionic species [Cp*Fe(h 5-P 5 SiEt 3)][B-(C 6 F 5) 4 ] (2), whose subsequent reaction with H 2 O yields the parent compound [Cp*Fe(h 5-P 5 H)][B(C 6 F 5) 4 ] (3). The synthesis of a carbon-substituted derivative [Cp*Fe(h 5-P 5 Me)][X] ([X] À = [FB(C 6 F 5) 3 ] À (4 a), [B(C 6 F 5) 4 ] À (4 b)) is achieved by methylation of 1 employing [Me 3 O][BF 4 ] and B(C 6 F 5) 3 or a combination of MeOTf and [Li(OEt 2) 2 ][B(C 6 F 5) 4 ]. The structural characterisation of these compounds reveals a slight envelope structure for the cyclo-P 5 R ligand. Detailed NMRspectroscopic studies suggest a highly dynamic behaviour and thus a distinct lability for 2 and 3 in solution. DFT calculations shed light on the electronic structure and bonding situation of this unprecedented class of compounds.

Substituted aromatic pentaphosphole ligands – a journey across the p-block

“…The 31 P{ 1 H} NMR spectra of most of the obtained products reveal complex AMM 0 XX 0 (4, 5), AA 0 BB 0 X ( 7), AA 0 MXX 0 (11), AA 0 MM 0 X (6, 9, 12) or even AA 0 M 2 M 0 2 X 2 X 0 2 (2) spin systems (see ESI †). However, 3, 8, 10 and 13 show a highly dynamic behavior in CD 2 Cl 2 solution which cannot be resolved, not even at À80 C. Similar dynamic broadening of signals has been observed for the parent compound 20 and might be caused by a tumbling process of the respective substituent around the P 5 ring. When comparing the 31 P{ 1 H} NMR spectra (Fig.…”

“…The P-P bond lengths within 2-13 are similar and in between the sum of the covalent radii of P-P single and double bonds. 31 As observed for the parent compound [Cp*Fe(h 5 -P 5 H)] + , 20 the substituents in the hetero-pentaphosphole complexes 2-7 and 9-13 are oriented in exo-fashion regarding the envelope of the P 5 ring (Fig. 1).…”

“…However, they compare well with that determined for the parent pentaphosphole complex [Cp*Fe(h 5 -P 5 H)] + (NICS(AE-1) zz ¼ À32.1/À31.2). 20 A rough correlation between the pyramidalization at P 1 and the computed NICS values is observed, although this effect is not much accentuated and has minor exceptions (see ESI †). Thus, we demonstrated the in situ electrophilic functionalization of 1 to be a highly versatile approach towards a variety of unprecedented hetero-pentaphosphole complexes.…”

“…8 Only recently, we succeeded in the synthesis of the rst transition metal complexes [Cp*Fe(h 5 -P 5 R)][B(C 6 F 5 ) 4 ] (IV, R ¼ H, Me, SiEt 3 ) featuring such pentaphosphole ligands. 20 While our previous approach is wellsuited to prepare the parent compound with a cyclo-P 5 H ligand, it is limited to group 14 electrophiles (such as CH 3 /SiEt 3 ) as introducible substituents. 21 Thus, we sought a more general strategy to electrophilically functionalize 1 which may also be applicable beyond the synthesis of the targeted hetero-pentaphosphole complexes to other heteroaromatic ligands.…”

Insertion of Phosphenium Ions into a Bicyclo[1.1.0]Tetraphosphabutane Iron Complex

“…Besides P 4 , the tetrahedral complex [Cp‴Ni(η 3 -P 3 )] also reacts with phosphenium cations by insertion into one P-P bond [ 26 ]. In contrast, [Cp*Fe(η 5 -P 5 )] reacts with main group electrophiles, such as, for instance, H + or CH 3 + with the formation of a P-E bond [ 27 ]. Our preliminary studies have shown that 1 reacts with HBF 4 , leading to the protonation of one of the wing tip phosphorus atoms [ 12 ].…”