Michael Franz Lappert. 31 December 1928 — 28 March 2014

Abstract

Michael Lappert was one of the giants of twentieth-century organometallic chemistry. His research, carried out over six decades and leading to about 800 publications, had a profound and influential effect on the field, and his contributions covered almost every block of the Periodic Table. His early reputation was established by his extensive studies in boron chemistry exemplified by the reports of BCl 4 − , BN cyclobutadiene analogues, triborylamines, BCl 3 -catalysed ortho -Claisen rearrangements and evidence for restricted rotation about the B–N bond in aminoboranes. He had a lifelong interest in amides, including those of carbon, and especially electron-rich olefins, which remarkably were the ready source of numerous transition-metal carbene complexes. The last could also be obtained directly from the Vilsmeier reagent. He was the first to show that a carbene complex may act as an initiator of olefin metathesis. Later interests concerned the syntheses of new types of compound from all blocks of the Periodic Table driven by his imaginative use of new types of ligand (either sterically crowded or having no β-hydrogen atoms, often including SiMe 3 or Bu t substituents to confer lipophilicity). The use of CH n SiMe (3− n ) ( n = 0, 1 or 2) to stabilize transition-metal alkyl compounds was a major advance, because at the time stable homoleptic (a term he introduced) transition-metal alkyl compounds were unknown. He showed that the −CH(SiMe 3 ) 2 ligand could stabilize both low-coordinate transition metal and lanthanide compounds. Similarly, carbene analogues of the Main Group 14 elements germanium, tin and lead were obtained. Surprisingly in the solid state, these species were weakly dimerized (for example R 2 Sn=SnR 2 ), and unexpectedly exhibited a pyramidalized geometry at the heavy element. The latter had very significant bonding implications, because it differed fundamentally from the well-known planar structure of the corresponding alkenes. The first persistent or stable paramagnetic heavier Main Group element species MR 2 (M = P or As) and MR 3 (M = Ge or Sn) were also obtained while parallel work using −N(SiMe 3 ) 2 resulted in the corresponding Main Group amido derivatives. Other lipophilic ligands, such as β-diketiminates, were also widely used, as were bulky aryloxo and thiolato ligands, to obtain stable low-coordinate Main Group species. The first examples of d- and f-block species containing bridging alkyl groups were described. Those who worked with him cited his vast knowledge and supportive low-key advisory style, which ensured a contented and productive laboratory atmosphere. In addition to his scientific work, he was deeply interested in opera, literature and the theatre, about which he could talk knowledgeably.