Complex sentence: In Paris he conducted the world premieres of Debussy's "Pelléas et Mélisande", Massenet's "Grisélidis" and Charpentier's "Louise", and, at Covent Garden, the British premieres of operas by Saint-Saëns and Massenet.
Split into simpler sentences: In Paris he conducted the world premieres of Debussy's "Pelléas et Mélisande", Massenet's "Grisélidis" and Charpentier's "Louise". At Covent Garden, he led the British premieres of operas by Saint-Saëns and Massenet.