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Molecular-level understanding of metal-mediated white phosphorus (P4 ) activation is meaningful but challenging because of its direct relevance to the conversion of P4 into useful organophosphorus compounds as well as the complicated and unforeseeable cleavage process of P-P bonds. The related study, however, has still rarely been achieved to date. Here, a theoretical insight into the step-by-step process of three P-P bond cleavage/four P-C bond formation for [P3 +P1 ]-fragmentation of P4 mediated by lutetacyclopentadienes is reported. The unique charge-separated intermediate and the intermolecular cooperation between two lutetacyclopentadienes play a vital role in the subsequent P-P/P-C bond breaking/forming. It is found that, although the first P-C formation is involved in the assembly of the cyclo-P3 [R4 C4 P3 ]- unit, the construction of the aromatic five-membered P1 heterocycle [R4 C4 P]- is completed prior to the cyclo-P3 formation. The reaction mechanism has been carefully elucidated by analyses of the geometric structure, frontier molecular orbitals, bond index, and natural charge, which greatly broaden and enrich the general knowledge of the direct functionalization of P4 .

A series of butadienyl organomagnesium complexes, including 1-Li-4-(MgR)-butadienes, 1,4-bis(MgR)-butadienes, and 1-Mg-4-(MgR)-butadiene were synthesized starting with 1,4-dilithio butadienes via the transmetalation reaction between alkenyllithium bond and alkenylmagnesium bond. Single-crystal X-ray structural analysis of these butadienyl organomagnesiates revealed unique bonding modes. Study on their structural transformation demonstrated that 1-Li-4-(MgR)-butadiene is the key intermediate in the reaction process leading to the formation of 1,4-bis(MgR)-butadiene and 1-Mg-4-(MgR)-butadiene.

The selective C(sp3)−H bond functionalization is an ideal and atom-economical method in organic synthesis. In this work, 2-aminopyrimidines are generated from a Cu-catalyzed reaction between carbodiimides and diaryliodonium salts, by cleavage of four C(sp3)−H, one C−N, and one C=N bonds in the carbodiimides. It is the first triple C(sp3)−H bond functionalization neighboring a C=N bond. The selective synthesis of 2-aminopyrimidines is controlled by the amount of the diaryliodonium salts. The novel mechanism involving a C−N formation/1,5-H shift/1,7-H shift/6 π-electrocyclic ring-closing/aromatization is well elucidated by the detection of important intermediates and DFT calculations.

The Zn(OTf)2 -catalyzed guanylation/amidation from readily available amino acid esters and carbodiimides is achieved to provide efficiently various cyclic oxoguanidines, including 2-amino-1H-imidazol-5(4H)-ones and 2-aminoquinazolin-4(3H)-ones in medium-to-high yields. It is the first time that an ammonium salt has been used in a guanylation reaction. The application of cyclic oxoguanidines to provide the conjugated heterocyclic compounds via oxidative C-N formation or aldol reaction is explored. The reaction mechanism is well elucidated by the isolation and characterization of three important intermediates.

A variety of ester-substituted cyclopentadiene derivatives have been synthesized by one-pot reactions of 1,4-dilithio-1,3-butadienes, CO, and acid chlorides. Direct deprotonation of the ester-substituted cyclopentadienes with Ae[N(SiMe3 )2 ]2 (Ae=Ca, Sr, Ba) efficiently generated members of a new class of heavier alkaline earth (Ca, Sr, Ba) metallocenes in good to excellent yields. Single-crystal X-ray structural analysis demonstrated that these heavier alkaline earth metallocenes incorporated two intramolecularly coordinated ester pendants and multiply-substituted cyclopentadienyl ligands. The corresponding transition metal metallocenes, such as ferrocene derivatives and half-sandwich cyclopentadienyl tricarbonylrhenium complexes, could be generated highly efficiently by metathesis reactions. The multiply-substituted cyclopentadiene ligands bearing an ester pendant, and the corresponding heavier alkaline earth and transition-metal metallocenes, may have further applications in coordination chemistry, organometallic chemistry, and organic synthesis.

This study sheds light on the cleavage and reorganization of C(sp(3))-H and C=N bonds of carbodiimides in a three-component reaction of terminal alkynes, sulfur, and carbodiimides by a combination of methods including 1) isolation and X-ray analysis of six-membered-ring lithium species 2-S, 2) trapping of the oxygen-analogues (B-O and D-O) of both four-membered-ring intermediate B-S and ring-opening intermediate D-S, 3) deuterium labeling studies, and 4) theoretical studies. These results show that 1) the reaction rate-determining step is [2+2] cycloaddition, 2) the C=N bond cleavage takes place before C(sp(3))-H bond cleavage, 3) the hydrogen attached to C6 in 2-S originates from the carbodiimide, and 4) three types of new aza-heterocycles, such as 1,2-dihydrothiopyrimidines, N-acyl 2,3-dihydropyrimidinthiones, and 1,2-dihydropyrimidinamino acids are constructed efficiently based on 2-S. All results strongly support the idea that the reaction proceeds through [2+2] cycloaddition/4π electrocyclic ring-opening/1,5-H shift/6π electrocyclic ring-closing as key steps. The research strategy on the synthesis, isolation, and reactivity investigation of important intermediates in metal-mediated reactions not only helps achieve an in-depth understanding of reaction mechanisms but also leads to the discovery of new synthetically useful reactions based on the important intermediates.

5-Azaindoles either with three different substituents at their 2-, 4-, and 6-positions or with two identical substituents at their 2- and 6-positions and a different one at the 4-position, were obtained in good to excellent isolated yields by a zirconocene-mediated multicomponent process. Each reaction involved four organic partners, comprising a Si-tethered diyne, one tBuCN component, and two (either different or identical) nitriles. All these four components were combined through the action of a Cp(2)Zr(II) species into a three-ring fused Zr/Si-containing organometallic complex in a perfectly chemo- and regioselective manner. This multicomponent reaction process consisted of three reaction steps, all of which were made clear through the isolation and characterization of their corresponding organometallic intermediates: the zirconacyclopropene-azasilacyclopentadienes 2, the allenyl-aza-zirconacycles 3, and the three-ring fused complexes 6. X-ray single-crystal structural analyses of two three-ring fused Zr/Si-containing intermediates and two 5-azaindoles unambiguously showed the positions of the different substituents and the regioselectivity. Iminopyrrole derivatives could be also highly selectively prepared from a Si-tethered diyne and two different nitriles.

A zirconocene-mediated one-pot multicomponent synthesis process leading to the synthesis of pyrrolo[3,2-c]pyridine (5-azaindoles) and pyrrole derivatives has been developed starting from a silicon-tethered diyne and three or two different or identical organonitriles. Pyrrolo[3,2-c]pyridine and pyrrole derivatives with diverse structures and substitution patterns have been highly selectively prepared by this protocol. A wide variety of organonitriles and silicon-tethered diynes, either aliphatic or aromatic with both electron-withdrawing and -donating groups, have been used to afford 5-azaindoles and/or pyrroles in good-to-excellent isolated yields. A key intermediate formed in the Cp(2)Zr(II)-mediated reaction of one (PhC[triple bond]C)(2)SiMe(2), two molecules of iPrCN and one p-tolylCN was characterised by X-ray single-crystal structural analysis, which has allowed us to gain a good understanding of the reaction process.

Addition cyclization of 1,2,3,4-tetrasubstituted 1,4-dilithio-1,3-dienes (Type I) with four equivalents of various aromatic nitriles in the presence of hexamethylphosphoramide (HMPA) gives exclusively fully substituted pyridines in moderate to good yields. Similarly, trisubstituted pyridines can be prepared by the reaction of 2,3-dialkyl- or diaryl-substituted 1,4-dilithio-1,3-dienes (Type II) with nitriles. However, five- or six-membered-ring fused 2,3-disubstituted 1,4-dilithio-1,3-dienes (Type III) reacted with various aromatic and aliphatic nitriles without alpha-hydrogen atoms to afford tricyclic Delta1-bipyrrolines in high yields. The reaction of six-membered-ring fused 2,3-disubstituted 1,4-dilithio-1,3-diene (Type III) with 2-cyanopyridine afforded the corresponding pyridine, and no tricyclic Delta1-bipyrroline was observed. Seven-membered-ring fused dilithiodienes reacted with PhCN or trimethylacetonitrile to afford the corresponding pyridines in good yield. When 1,2,3,4-tetrasubstituted dilithio reagents (Type I) were treated with Me3SiCN, a tandem silylation/intramolecular substitution process readily occurred to yield siloles, whereas the reaction of 2,3-disubstituted dilithio reagents (Types II and III) with Me3SiCN gave rise to (Z,Z)-dienylsilanes with high stereoselectivity. These results revealed that the formation of tricyclic Delta1-bipyrrolines, pyridines, siloles, and (Z,Z)-dienylsilanes are strongly dependent on the substitution patterns of the dilithio butadienes and the nature of the nitriles employed.

The acid-base reactions between the rare-earth metal (Ln) tris-(ortho-N,N-dimethylaminobenzyl) complexes [Ln(CH 2 C 6 H 4 NMe 2 -o) 3 ] with one equivalent of the silylene-linked cyclopentadiene-amine ligand (C 5 Me 4 H)-SiMe2NH(C 6 H 2 Me 3 -2,4,6) afforded the corresponding half-sandwich aminobenzyl complexes [{Me 2 Si(C 5 Me 4 )-(NC6H2Me3-2,4,6))Ln(CH 2 C 6 H 4 NMe 2 -o)(thf)] (2-Ln) (Ln=Y, La, Pr, Nd, Sm, Gd, Lu) in 60-87 % isolated yields. The one-pot reaction between ScCl 3 and [Me2Si(C5Me4)(NC 6 H 2 Me 3 -2,4,6)]Li 2 followed by reaction with LiCH 2 C 6 H 4 NMe 2 -o in THF gave the scandium analogue [(Me 2 Si(C 5 Me 4 )-(NC 6 H 2 Me 3 -2,4,6))Sc(CH2C6H4NMe2-o)] (2-Sc) in 67 % isolated yield. 2-Sc could not be prepared by the acid-base reaction between [Sc(CH 2 C 6 H 4 NMe 2 -o) 3 ] and (C5Me4H)SiMe2NH(C 6 H 2 Me 3 -2,4,6). These half-sandwich rare-earth metal aminobenzyl complexes can serve as efficient catalyst precursors for the catalytic addition of various phosphine P-H bonds to carbodiimides to form a series of phosphaguanidine derivatives with excellent tolerability to aromatic carbon-halogen bonds. A significant increase in the catalytic activity was observed, as a result of an increase in the metal size with a general trend of La > Pr, Nd>Sm>Gd>Lu>Sc. The reaction of 2-La with 1 equiv of Ph 2 PH yielded the corresponding phosphide complex [{Me2Si(C 5 Me 4 )(NC6H2Me3-2,4,6)}La(PPh2)(thf)2] (4), which, on recrystallization from benzene, gave the dimeric analogue [(Me 2 Si(C 5 Me 4 )-(NC6H2Me3-2,4,6)}La(PPh2)]2 (5). Addition of 4 or 5 to iPrN=C=NiPr in THF yielded the phosphaguanidinate complex [(Me 2 Si(C 5 Me 4 )(NC 6 H 2 Me 3 -2,4,6)}La{iPrNC(PPh 2 )NiPr}(thf)] (6), which, on recrystallization from ether, afforded the ether-coordinated structurally characterizable analogue [{Me 2 Si(C5Me4)(NC 6 H 2 Me 3 -2,4,6)}La-(iPrNC(PPh2)NiPr}(OEt 2 )] (7). The reaction of 6 or 7 with Ph 2 PH in THF yielded 4 and the phosphaguanidine iPrN=C(PPh 2 )NHiPr (3 a). These results suggest that the catalytic formation of a phosphaguanidine compound proceeds through the nucleophilic addition of a phosphide species, which is formed by the acid-base reaction between a rare-earth metal o-dimethylaminobenzyl bond and a phosphine P-H bond, to a carbodiimide, followed by the protonolysis of the resultant phosphaguanidinate species by a phosphine P-H bond. Almost all of the rare earth complexes reported this paper were structurally characterized by X-ray diffraction studies.